and detect leaked temporary files and mount entries after each test run.

Background

Currently we have several testing-related problems that are
all connected to /tmp and similar directories:

Problem 1: many tests create temporary files for each run. Usually
tests are careful to remove them on teardown, but due to bugs, many kind
of tests, test processes being hard-killed (SIGKILL, or SIGSEGV) and
other reasons, in practice this cleanup does not work 100% reliably and
there is steady growth of files leaked on /tmp on testnodes.

Problem 2: due to using shared /tmp and /dev/shm, the isolation in
between different test runs of potentially different users is not
strong. For example @jerome reports that due to leakage of faketime's
shared segments separate test runs affect each other and fail:
https://erp5.nexedi.net/bug_module/20211125-1C8FE17

Problem 3: many tests depend on /tmp being a tmpfs instance. This are for
example wendelin.core tests which are intensively writing to database,
and, if /tmp is resided on disk, timeout due to disk IO stalls in fsync
on every commit. The stalls are as much as >30s and lead to ~2.5x overall
slowdown for test runs. However the main problem is spike of increased
latency which, with close to 100% probability, always render some test
as missing its deadline. This topic is covered in
https://erp5.com/group_section/forum/Using-tmpfs-for--tmp-on-testnodes-JTocCtJjOd

--------

There are many ways to try to address each problem separately, but they
all come with limitations and drawbacks. We discussed things with @tomo
and @jerome, and it looks like that all those problems can be addressed
in one go if we run tests under user namespaces with private mounts for
/tmp and /dev/shm.

Even though namespaces is generally no-go in Nexedi, they seem to be ok
to use in tests. For example they are already used via private_tmpfs
option in SlapOS:

https://lab.nexedi.com/nexedi/slapos/blob/1876c150/slapos/recipe/librecipe/execute.py#L87-103
https://lab.nexedi.com/nexedi/slapos/blob/1876c150/software/neoppod/instance-neo-input-schema.json#L121-124
https://lab.nexedi.com/nexedi/slapos/blob/1876c150/software/neoppod/instance-neo.cfg.in#L11-16
https://lab.nexedi.com/nexedi/slapos/blob/1876c150/software/neoppod/instance-neo.cfg.in#L30-34
https://lab.nexedi.com/nexedi/slapos/blob/1876c150/software/neoppod/instance-neo.cfg.in#L170-177
...
https://lab.nexedi.com/nexedi/slapos/blob/1876c150/stack/erp5/instance-zope.cfg.in#L227-230

Thomas says that using private tmpfs for each test would be a better
solution than implementing tmpfs for whole /tmp on testnodes. He also
reports that @jp is OK to use namespaces for test as long as there is a
fallback if namespaces aren't available.

-> So let's do that: teach nxdtest to run each test case in its own
private environment with privately-mounted /tmp and /dev/shm if we can
detect that user namespaces are available. In an environment where user
namespaces are indeed available this addresses all 3 problems because
isolation and being-tmpfs are there by design, and even if some files
will leak, the kernel will free everything when test terminates and the
filesystem is automatically unmounted. We also detect such leakage and
report a warning so that such problems do not go completely unnoticed.

Implementation

We leverage unshare(1) for simplicity. I decided to preserve uid/gid
instead of becoming uid=0 (= `unshare -Umr`) for better traceability, so
that it is clear from test output under which real slapuser a test is
run(*). Not changing uid requires to activate ambient capabilities so
that mounting filesystems, including FUSE-based needed by wendelin.core,
continue to work under regular non-zero uid. Please see
https://git.kernel.org/linus/58319057b784 for details on this topic. And
please refer to added trun.py for details on how per-test namespace is setup.

Using FUSE inside user namespaces requires Linux >= 4.18 (see
https://git.kernel.org/linus/da315f6e0398 and
https://git.kernel.org/linus/8cb08329b080), so if we are really to use
this patch we'll have to upgrade kernel on our testnodes, at least where
wendelin.core is used in tests.

"no namespaces" detection is implemented via first running `unshare ...
true` with the same unshare options that are going to be used to create
and enter new user namespace for real. If that fails, we fallback into
"no namespaces" mode where no private /tmp and /dev/shm are mounted(%).

(*) for example nxdtest logs information about the system on startup:

    date:   Mon, 29 Nov 2021 17:27:04 MSK
    xnode:  slapuserX@test.node
    ...

(%) Here is how nxdtest is run in fallback mode on my Debian 11 with
    user namespaces disabled via `sysctl kernel.unprivileged_userns_clone=0`

    (neo) (z-dev) (g.env) kirr@deca:~/src/wendelin/nxdtest$ nxdtest
    date:   Thu, 02 Dec 2021 14:04:30 MSK
    xnode:  kirr@deca.navytux.spb.ru
    uname:  Linux deca 5.10.0-9-amd64 #1 SMP Debian 5.10.70-1 (2021-09-30) x86_64
    cpu:    Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz

    >>> pytest
    $ python -m pytest
    # user namespaces not available. isolation and many checks will be deactivated.    <--- NOTE
    ===================== test session starts ======================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.10.0, pluggy-0.13.1
    rootdir: /home/kirr/src/wendelin/nxdtest
    plugins: timeout-1.4.2
    collected 23 items

    nxdtest/nxdtest_pylint_test.py ....                      [ 17%]
    nxdtest/nxdtest_pytest_test.py ...                       [ 30%]
    nxdtest/nxdtest_test.py ......xx                         [ 65%]
    nxdtest/nxdtest_unittest_test.py ........                [100%]

    ============= 21 passed, 2 xfailed in 2.67 seconds =============
    ok      pytest  3.062s  # 23t 0e 0f 0s
    # ran 1 test case:  1·ok

/helped-by @tomo
/helped-and-reviewed-by @jerome
/reviewed-on nexedi/nxdtest!13

Also log if master told us that we have nothing to do, and if the mode to run is local.

This should make it a bit more clear what is going on just by looking at
nxdtest log. See previous patch for more details and context.

For the reference: here is how updated output looks like in the normal case:

    date:   Thu, 09 Dec 2021 04:20:37 CET
    xnode:  slapuser7@rapidspace-testnode-001
    uname:  Linux rapidspace-testnode-001 4.9.0-16-amd64 #1 SMP Debian 4.9.272-1 (2021-06-21) x86_64
    cpu:    Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz
    # running for test_result_module/20211209-170FD3998

    >>> pytest
    $ python -m pytest
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /srv/slapgrid/slappart7/t/dfp/soft/47cc86af27d234f0464630f2a0d22a6f/parts/zodbtools-dev
    collected 46 items

    zodbtools/test/test_analyze.py .                                         [  2%]
    zodbtools/test/test_commit.py ..                                         [  6%]
    zodbtools/test/test_dump.py ...                                          [ 13%]
    zodbtools/test/test_restore.py ..                                        [ 17%]
    zodbtools/test/test_tidrange.py .............................            [ 80%]
    zodbtools/test/test_zodb.py .........                                    [100%]

    ========================== 46 passed in 9.15 seconds ===========================
    ok      pytest  12.433s # 46t 0e 0f 0s
    # ran 1 test case:  1·ok

/reviewed-by @jerome
/reviewed-on nexedi/nxdtest!15

Nxdtest logs system information (bd91f6f1 "Include system information
into log output") and run summary at the end (9f413221 "Emit run summary
at the end"). However all that information currently is printed only if
master is successfully connected and actually tells to run the tests.

This behaviour is not very useful, because if nxdtest log output on
testnode is empty, it is not clear - whether it was "we have to do
nothing", or nxdtest stuck somewhere or something else.

For example
https://nexedijs.erp5.net/#/test_result_module/20211208-47D165B7/12 is
currently marked as Running for many long hours already. And the log on
testnode regarding nxdtest run is just:

    2021-12-08 15:42:17,314 INFO     $ PATH=/srv/slapgrid/slappart13/srv/slapos/soft/2956f419073cb2249ed953507fa6b173/bin:/opt/slapos/parts/bison/bin:/opt/slapos/parts/bzip2/bin:/opt/slapos/parts/gettext/bin:/opt/slapos/parts/glib/bin:/opt/slapos/parts/libxml2/bin:/opt/slapos/parts/libxslt/bin:/opt/slapos/parts/m4/bin:/opt/slapos/parts/ncurses/bin:/opt/slapos/parts/openssl/bin:/opt/slapos/parts/pkgconfig/bin:/opt/slapos/parts/python2.7/bin:/opt/slapos/parts/readline/bin:/opt/slapos/parts/sqlite3/bin:/opt/slapos/parts/swig/bin:/opt/slapos/bin:/opt/slapos/parts/patch/bin:/opt/slapos/parts/socat/bin:/usr/bin:/usr/sbin:/sbin:/bin SLAPOS_TEST_LOG_DIRECTORY=/srv/slapgrid/slappart13/var/log/testnode/dgd-xStX9safSG SLAPOS_TEST_SHARED_PART_LIST=/srv/slapgrid/slappart13/srv/shared:/srv/slapgrid/slappart13/t/dgd/shared /bin/sh /srv/slapgrid/slappart13/t/dgd/i/0/bin/runTestSuite --master_url $DISTRIBUTOR_URL --revision slapos=13977-ec686a708633f689382426063c21efbe3b2eab04,slapos.core=8698-91edab77ed36c160da8017cfdc1673fe7a8e10de --test_node_title rapidspace-testnode-008-3Nodes-DEPLOYTASK0 --test_suite SLAPOS-SR-TEST --test_suite_title SlapOS.SoftwareReleases.IntegrationTest-kirr.Python2 --project_title 'Rapid.Space Project'

without anything else.

With this patch nxdtest would print system information and report how many
tests it had run, if its invocation did not stuck.

In this patch we only move code that calls system_info and defer summary log
before code that connects to master. In the following patch we'll add more
logging around connecting to master.

/reviewed-by @jerome
/reviewed-on nexedi/nxdtest!15

Sometimes there is zero testcases to be executed on testnodes, and
log output from nxdtest is just

    date:   Wed, 10 Nov 2021 12:31:50 MSK
    xnode:  kirr@deca.navytux.spb.ru
    uname:  Linux deca 5.10.0-9-amd64 #1 SMP Debian 5.10.70-1 (2021-09-30) x86_64
    cpu:    Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz

it is not clear from such output did the run ended or the test got
stuck. After this patch it becomes

    date:   Wed, 10 Nov 2021 12:31:50 MSK
    xnode:  kirr@deca.navytux.spb.ru
    uname:  Linux deca 5.10.0-9-amd64 #1 SMP Debian 5.10.70-1 (2021-09-30) x86_64
    cpu:    Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz
    # ran 0 test cases.

And in general, when there are several testcases to be run, it is helpful to
indicate end of such run and to print brief summary of result status for all
ran test cases. Example output:

    wendelin.core$ nxdtest -k test.wcfs
    date:   Wed, 10 Nov 2021 12:35:34 MSK
    xnode:  kirr@deca.navytux.spb.ru
    uname:  Linux deca 5.10.0-9-amd64 #1 SMP Debian 5.10.70-1 (2021-09-30) x86_64
    cpu:    Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz
    >>> test.wcfs/fs:1
    ...
    ok      test.wcfs/fs:1  25.035s # 35t 0e 0f 0s

    >>> test.wcfs/fs:2
    ...
    ok      test.wcfs/fs:2  21.033s # 35t 0e 0f 0s

    >>> test.wcfs/fs:
    ...
    ok      test.wcfs/fs:   21.056s # 35t 0e 0f 0s
    # ran 3 test cases:  3·ok

/reviewed-by @jerome
/reviewed-on nexedi/nxdtest!12

This parses pylint output with a simple regexp and counts one failure per
message reported.

This has not been tested yet, but we decided to apply this commit already.

/acked-by @kirr
/reviewed-on nexedi/nxdtest!11

When using compile with the actual file path, we can have better tracebacks
in case of errors.

before:

    Traceback (most recent call last):
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/bin/nxdtest", line 22, in <module>
        sys.exit(nxdtest.main())
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/parts/nxdtest/nxdtest/__init__.py", line 142, in main
        tenv = loadNXDTestFile('.nxdtest')
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/parts/nxdtest/nxdtest/__init__.py", line 75, in loadNXDTestFile
        six.exec_(src, g)
      File "<string>", line 77, in <module>
    NameError: name 'Pylint' is not defined

after:

    Traceback (most recent call last):
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/bin/nxdtest", line 22, in <module>
        sys.exit(nxdtest.main())
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/parts/nxdtest/nxdtest/__init__.py", line 142, in main
        tenv = loadNXDTestFile('.nxdtest')
      File "/srv/slapgrid/slappart3/srv/runner/software/9544feb19475590d240ba2d32743c0a0/parts/nxdtest/nxdtest/__init__.py", line 75, in loadNXDTestFile
        six.exec_(compile(src, os.path.realpath(path), 'exec'), g)
      File "/srv/slapgrid/slappart3/srv/runner/instance/slappart8/var/nxdtest/.nxdtest", line 77, in <module>
        summaryf=Pylint.summary,
    NameError: name 'Pylint' is not defined

/reviewed-by @kirr
/reviewed-in nexedi/nxdtest!10

For every TestCase nxdtest spawns test process to run with stdout/stderr
redirected to pipes that nxdtest reads. Nxdtest, in turn, tees those
pipes to its stdout/stderr until the pipes become EOF. If the test
process, in turn, spawns other processes, those other processes will
inherit opened pipes, and so the pipes won't become EOF untill _all_
spawned test processes (main test process + other processes that it
spawns) exit. Thus, if there will be any process, that the main test
process spawned, but did not terminated upon its own exit, nxdtest will
get stuck waiting for pipes to become EOF which won't happen at all if a
spawned test subprocess persists not to terminate.

I hit this problem for real on a Wendelin.core 2 test - there the main
test processes was segfaulting and so did not instructed other spawned
processes (ZEO, WCFS, ...) to terminate. As the result the whole test
was becoming stuck instead of being promptly reported as failed:

    runTestSuite: Makefile:175: recipe for target 'test.wcfs' failed
    runTestSuite: make: *** [test.wcfs] Segmentation fault
    runTestSuite: wcfs: 2021/08/09 17:32:09 zlink [::1]:52052 - [::1]:23386: recvPkt: EOF
    runTestSuite: E0809 17:32:09.376800   38082 wcfs.go:2574] zwatch zeo://localhost:23386: zlink [::1]:52052 - [::1]:23386: recvPkt: EOF
    runTestSuite: E0809 17:32:09.377431   38082 wcfs.go:2575] zwatcher failed -> switching filesystem to EIO mode (TODO)
    <LONG WAIT>
    runTestSuite: PROCESS TOO LONG OR DEAD, GOING TO BE TERMINATED

-> Fix it.

/reviewed-by @jerome
/reviewed-on nexedi/nxdtest!9

re.match only find matches where the pattern appears at the beginning of
the string, whereas re.search matches if the pattern appears anywhere in
the string. This is behavior is consistent with pytest, go test and ERP5's
runUnitTest

For more details, see the discussion from !6 (comment 121409)

/reviewed-on: !8

The reason is that with threading.Thread if exception happens in that
spawned thread, this error is not propagated to main driver, while with
sync.WorkGroup an exception from any spawned worker is propagated back
to main. For example with the following injected error

    --- a/nxdtest/__init__.py
    +++ b/nxdtest/__init__.py
    @@ -267,6 +267,7 @@ def main():

     # tee, similar to tee(1) utility, copies data from fin to fout appending them to buf.
     def tee(ctx, fin, fout, buf):
    +    1/0
         while 1:

before this patch nxdtest behaves like ...

    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ nxdtest
    date:   Tue, 24 Nov 2020 14:55:08 MSK
    xnode:  kirr@deco.navytux.spb.ru
    uname:  Linux deco 5.9.0-2-amd64 #1 SMP Debian 5.9.6-1 (2020-11-08) x86_64
    cpu:    Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz

    >>> pytest
    $ python -m pytest
    Exception in thread Thread-2:
    Traceback (most recent call last):
      File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
        self.run()
      File "/usr/lib/python2.7/threading.py", line 754, in run
        self.__target(*self.__args, **self.__kwargs)
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 270, in tee
        1/0
    ZeroDivisionError: integer division or modulo by zero

    Exception in thread Thread-1:
    Traceback (most recent call last):
      File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
        self.run()
      File "/usr/lib/python2.7/threading.py", line 754, in run
        self.__target(*self.__args, **self.__kwargs)
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 270, in tee
        1/0
    ZeroDivisionError: integer division or modulo by zero

    error   pytest  0.583s  # 1t 1e 0f 0s
    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ echo $?
    0

Here the error in another thread is only printed, but nxdtest is not aborted.
Above it reported "error", but e.g. when testing pygolang/py3 and raising an
error in tee it even reported it was succeeding
( nexedi/nxdtest!6 (comment 121393) ):

    slapuser34@vifibcloud-rapidspace-hosting-007:~/srv/runner/instance/slappart0$ ./bin/runTestSuite
    date:   Tue, 24 Nov 2020 12:51:23 MSK
    xnode:  slapuser34@vifibcloud-rapidspace-hosting-007
    uname:  Linux vifibcloud-rapidspace-hosting-007 4.19.0-6-amd64 #1 SMP Debian 4.19.67-2+deb10u2 (2019-11-11) x86_64
    cpu:    Intel(R) Xeon(R) CPU E5-2678 v3 @ 2.50GHz

    >>> thread
    $ python -m pytest
    Exception in thread Thread-1:
    Traceback (most recent call last):
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 926, in _bootstrap_inner
        self.run()
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 870, in run
        self._target(*self._args, **self._kwargs)
      File "/srv/slapgrid/slappart34/srv/runner/software/44fe7dd3f13ecd100894c6368a35c055/parts/nxdtest/nxdtest/__init__.py", line 268, in tee
        fout.write(data)
    TypeError: write() argument must be str, not bytes

    ok      thread  9.145s  # 1t 0e 0f 0s

    >>> gevent
    $ gpython -m pytest
    Exception in thread Thread-3:
    Traceback (most recent call last):
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 926, in _bootstrap_inner
        self.run()
      File "/srv/slapgrid/slappart34/srv/runner/shared/python3/5497998c60d97cbbf748337ccce21db2/lib/python3.7/threading.py", line 870, in run
        self._target(*self._args, **self._kwargs)
      File "/srv/slapgrid/slappart34/srv/runner/software/44fe7dd3f13ecd100894c6368a35c055/parts/nxdtest/nxdtest/__init__.py", line 268, in tee
        fout.write(data)
    TypeError: write() argument must be str, not bytes

    ok      gevent  21.980s # 1t 0e 0f 0s

After this patch nxdtest correctly handles and propagates an error originating
in spawned thread back to main driver:

    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ nxdtest
    date:   Tue, 24 Nov 2020 14:54:19 MSK
    xnode:  kirr@deco.navytux.spb.ru
    uname:  Linux deco 5.9.0-2-amd64 #1 SMP Debian 5.9.6-1 (2020-11-08) x86_64
    cpu:    Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz

    >>> pytest
    $ python -m pytest
    Traceback (most recent call last):
      File "/home/kirr/src/wendelin/venv/z4-dev/bin/nxdtest", line 11, in <module>
        load_entry_point('nxdtest', 'console_scripts', 'nxdtest')()
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 230, in main
        wg.wait()
      File "golang/_sync.pyx", line 237, in golang._sync.PyWorkGroup.wait
        pyerr_reraise(pyerr)
      File "golang/_sync.pyx", line 217, in golang._sync.PyWorkGroup.go.pyrunf
        f(pywg._pyctx, *argv, **kw)
      File "/home/kirr/src/wendelin/nxdtest/nxdtest/__init__.py", line 270, in tee
        1/0
    ZeroDivisionError: integer division or modulo by zero
    (neo) (z4-dev) (g.env) kirr@deco:~/src/wendelin/nxdtest$ echo $?
    1

NOTE sync.WorkGroup requires every worker to handle context cancellation, so
that whenever there is an error, all other workers are canceled. We add such
cancellation handling to tee but only lightly: before going to block in
read/write syscalls we check for whether ctx is canceled or not. However the
proper handling would be to switch file descriptors into non-block mode and to
select at every IO point on both potential IO events and potential
cancellation. This is left as TODO for the future.

/reviewed-on nexedi/nxdtest!7

These are the necessary changes to run `SlapOS.Eggs.UnitTest-*` and `SlapOS.SoftwareReleases.IntegrationTest-*` using nxdtest

See merge request nexedi/nxdtest!6

/reviewed-by @kirr

If test program output on stderr (which is unbuffered), the
output of the test program will appear before output from nxdtest
advertising the program that is about to be executed, because nxdtest
stdout is buffered (testnode does not set PYTHONUNBUFFERED, and eventhough
nxdtest sets PYTHONUNBUFFERED in its own environ, this only applies to sub
processes)

While pytest sends everything in stdout, some other programs send on stderr.

While treating output as text would not really be impossible, treating it
as bytes seems a better choice because:
 - we don't have to make assumptions about what output encoding the test
   program is using for output
 - `tee` can just read stream output bytes by bytes without having to worry
   about multi-bytes characters
 - testnode protocol uses xmlrpc.client.Binary, which uses bytes.

Because using bufsize=1 implies reading subprocess output as text, we use
bufsize=0 instead in the subprocess.Popen call, to prevent buffering.

To make manipulation of strings and bytes easier, we add a dependency on
pygolang, so that we can use its strings utility functions.

Also add a few tests to verify general functionality.

For example wendelin.core 2 uses pytest_unconfigure to unmount wcfs
servers that it spawned:

https://lab.nexedi.com/kirr/wendelin.core/blob/1be4d730/conftest.py#L27-53

This usually leads to some test as shown in added test.

-> Skip that text backwards and actually detect pytest summary line
instead of returning empty dict, because empty dict forces Nexedi ERP5
to treat such test run to have UNKNOWN status, e.g.

https://erp5.nexedi.net/test_result_module/20201108-C170850/11

/cc @jerome
/reviewed-on nexedi/nxdtest!5

This allows to establish tests for Nxdtest itself under Nexedi testing
infrastructure.

/cc @jerome
/reviewed-on nexedi/nxdtest!4

lab.nexedi.com/kirr/nxdtest -> lab.nexedi.com/nexedi/nxdtest

nexedi/slapos!839 (comment 119120)
nexedi/slapos!839 (comment 119142)

/cc @jerome
/reviewed-on nexedi/nxdtest!3

/cc @jerome
/reviewed-on nexedi/nxdtest!1

Verify pytest summary-parsing functionality.

Create real nxdtest module, so that things could be imported from there.
As the result switch `nxdtest` program from scripts to entry_point.

Here is e.g. corresponding summary:

    ===== 12 failed, 14 passed, 4 xfailed, 12 error in 19.58 seconds =====

When checking logs on testnode, it is very useful to know which kernel
version is running inside (wendelin.core uses FUSE and depends on having
patched FUSE module for kernels < 5.2), which CPU is there, etc.

Format of printed output follows go benchmarking format and coincides
with start of `neotest info-local` (see footers on figures in
http://navytux.spb.ru/~kirr/neo.html and here:
https://lab.nexedi.com/kirr/neo/blob/1f26678b/go/neo/t/neotest#L585-874)

- To list which tests are in there,
- To execute only selected tests.

Apply only to local mode.
Very handy for debugging.

We started to print test result summary line for a testcase run since
0153635b (Teach nxdtest to run tests locally). However it is not present
in log when nxdtest is run under master. -> Include summary lines
everywhere for uniformity, with reason similar to bd1333bb (log += title
and argv for ran testcase).

This reverts commit 34e96b1d. Reason for revert is that since bd1333bb
(log += title and argv for ran testcase) we always emit details of
to-be-run command to log in the beginning of testcase run.

We started to display command and envadj in the log in the previous
patch. However only command - without envadj - was reported to master
for test result. -> Make it uniform: include envadj into details
everywhere.

When there are several or many testcases, it is hard to understand - by
seeing just log or console output - which part of the test suite was
running. It also helps to see the exact command that was spawned.

Example output for pygolang. Before:

    (neo) (z-dev) (g.env) kirr@deco:~/src/tools/go/pygolang$ nxdtest
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ssssss.sssssss                                   [100%]

    ==================== 99 passed, 13 skipped in 5.42 seconds =====================
    ok      thread  5.656s  # 112t 0e 0f 13s
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ..............                                   [100%]

    ========================= 112 passed in 17.35 seconds ==========================
    ok      gevent  17.768s # 112t 0e 0f 0s

After:

(neo) (z-dev) (g.env) kirr@deco:~/src/tools/go/pygolang$ nxdtest

    >>> thread
    $ python -m pytest
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ssssss.sssssss                                   [100%]

    ==================== 99 passed, 13 skipped in 5.27 seconds =====================
    ok      thread  5.508s  # 112t 0e 0f 13s

    >>> gevent
    $ gpython -m pytest
    ============================= test session starts ==============================
    platform linux2 -- Python 2.7.18, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
    rootdir: /home/kirr/src/tools/go/pygolang
    collected 112 items

    golang/_gopath_test.py ..                                                [  1%]
    golang/context_test.py ..                                                [  3%]
    golang/cxx_test.py ..                                                    [  5%]
    golang/errors_test.py ........                                           [ 12%]
    golang/fmt_test.py ...                                                   [ 15%]
    golang/golang_test.py ................................................   [ 58%]
    golang/io_test.py .                                                      [ 58%]
    golang/strconv_test.py ..                                                [ 60%]
    golang/strings_test.py .....                                             [ 65%]
    golang/sync_test.py .............                                        [ 76%]
    golang/time_test.py ........                                             [ 83%]
    golang/pyx/build_test.py ...                                             [ 86%]
    golang/pyx/runtime_test.py .                                             [ 87%]
    gpython/gpython_test.py ..............                                   [100%]

    ========================= 112 passed in 17.32 seconds ==========================
    ok      gevent  17.729s # 112t 0e 0f 0s

failure is assertion failure.
error is any other error.

Source: https://docs.python.org/3/library/unittest.html#organizing-test-code
-> "If the test fails, an exception will be raised ... identify the test
case as a failure. Any other exceptions will be treated as errors"

While searching ERP5 code for failure_count to clarify its meaning, I've
also discovered expected_failures and unexpected_successes (*) so they
are also added to the table.

(*) see e.g. https://lab.nexedi.com/nexedi/erp5/blob/1e31c091/product/ERP5Type/tests/ERP5TypeTestSuite.py#L6-8

Instead of just traceback saying that e.g. "No such command" without
information which command it was tried to spawn, stderr will now include
what was tried to be run. This makes diagnostic easier.

Many project that use pytest for testing won't need to redefine it over
and over again in their .nxdtest file.

It is very handy to debug both .nxdtest and nxdtest tool itself, and to
be able to run tests locally during development instead of (in addition
to) waiting for the test result from test nodes.

-> Teach nxdtest to run and report tests locally if no --master_url was
provided.

Idea is taken from runTestSuite.in from NEO, Cython+, Buildout and Rina:

https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/runTestSuite.in#L95-105
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/runTestSuite.in#L55-75
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/neoppod/stress-testing/runTestSuite.in#L17-37
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/cython-test/runTestSuite.in#L38-58
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/buildout-testing/runTestSuite.in#L21-39
https://lab.nexedi.com/nexedi/slapos/blob/3b14e028/software/build-rina/runTestSuite.in#L29-49

Instead of copying code over and over again, let's stick to UNIX
approach and make it to be in one tool only that does its job
(hopefully) good.

Previously, if --master_url was not provided, the program would crash
with UnboundLocalError for status, since for that case list of tests was
empty. Fix it by moving status initialization higher by one level.

See next patch where we'll add meaning for nxdtest run with no
--master_url set.

It is frequently needed to set some environment variable without
completely resetting everything else in the environment, because that
everything else can carry settings like PATH, PYTHONPATH, RPATH, etc for
the program to be able to run at all.

See nexedi/pygolang@b938af8b for recent example.

After previous patch that summary function is no-longer used, is
specific to NEO/py and so should be defined in .nxdtest file in that
project. lab.nexedi.com/kirr/neo will be adjusted correspondingly.

Make the tool generic: load list of testcases to run from .nxdtest file
and process the correspondingly. See added top-level documentation for
details.

Amends e9cc7e07 (Add minimal packaging setup)

So that nxdtest could be installed as egg via pip or buildout.

We will use it as the base for nxdtest.
Original history:

neo@51b18490
neo@f67c147d
neo@0e28fbb8