This will be used to implement both wcfs service and wcfs promise.

* master:
  tests: Don't try to access db.storage when automatically closing connections
  bigfile/py: Garbage-collect BigFile <=> BigFileH cycles
  bigfile/py: Move PyVMA's support for cyclic GC close to pyvma_dealloc
  t/tfault-run: Require bash
  t/tfault-run: Clear state from previous run before starting
  Add way to run tests via nxdtest

- it is more logical
- this way !wcfs tests don't try to excerceise wcfs functionality (and
  unexpectedly spawn wcfs server).

DB.close() does `del self.storage`.

https://github.com/zopefoundation/ZODB/blob/5.6.0-14-g0eae10cd0/src/ZODB/DB.py#L646

This way if DB was closed, but some conn(s) were not, it will crash in
teardown as e.g. below:

    _____________ ERROR at teardown of test_bigfile_zblk1_zdata_reuse ______________

        def teardown_module():
    >       testdb.teardown()

    bigfile/tests/test_filezodb.py:58:
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    self = <wendelin.lib.testing.TestDB_ZEO object at 0x7fb9c0216350>

        def teardown(self):
            # close connections that test code forgot to close
            for connref, tb in self.connv:
                conn = connref()
                if conn is None:
                    continue
                if not conn.opened:
                    continue    # still alive, but closed
                print("W: testdb: teardown: %s left not closed by test code"
                      "; opened by:\n%s" % (conn, tb), file=sys.stderr)

                db = conn.db()
    >           stor = db.storage
    E           AttributeError: 'DB' object has no attribute 'storage'

    lib/testing.py:217: AttributeError

The fix is simple - don't use db.storage at all, because it is not actually used in that code.

- use +D to request recursive search of everything under mntpt
- use -w to avoid seeing many-many warnings in case there are stale FUSE mounts.

DB.close() does `del self.storage`.

https://github.com/zopefoundation/ZODB/blob/5.6.0-14-g0eae10cd0/src/ZODB/DB.py#L646

This way if DB was closed, but some conn(s) were not, it will crash in
teardown as e.g. below:

    _____________ ERROR at teardown of test_bigfile_zblk1_zdata_reuse ______________

        def teardown_module():
    >       testdb.teardown()

    bigfile/tests/test_filezodb.py:58:
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    self = <wendelin.lib.testing.TestDB_ZEO object at 0x7fb9c0216350>

        def teardown(self):
            # close connections that test code forgot to close
            for connref, tb in self.connv:
                conn = connref()
                if conn is None:
                    continue
                if not conn.opened:
                    continue    # still alive, but closed
                print("W: testdb: teardown: %s left not closed by test code"
                      "; opened by:\n%s" % (conn, tb), file=sys.stderr)

                db = conn.db()
    >           stor = db.storage
    E           AttributeError: 'DB' object has no attribute 'storage'

    lib/testing.py:217: AttributeError

The fix is simple - don't use db.storage at all, because it is not actually used in that code.

Depends on custom patch to remember SSL credentials on NEO Client, and
also on patches to rework neo:// URLs to not keep credentials inside
query.

neo@b9a42957
neo@8c974485
neo@a2f192cb

This way when wcfs is started via _start it also takes default options
into account. Noticid while running test_join with
$WENDELIN_CORE_WCFS_OPTIONS set and not propagated to spawned wcfs.

go123 update is NFC.

Since ZBigFile keeps references to fileh objects that are created
through it it forms a file <=> fileh cycle that is not collected without
cyclic GC:

https://lab.nexedi.com/nexedi/wendelin.core/blob/v0.13-52-ga702d41/bigfile/file_zodb.py#L497
https://lab.nexedi.com/nexedi/wendelin.core/blob/v0.13-52-ga702d41/bigfile/file_zodb.py#L566-571

We did not noticed this leak until now because it is small, but with
upcoming wendelin.core 2 it is important to release a fileh, because
there is WCFS connection associated with fileh, and if fileh is not
released, that connection also stays alive, keeping on-WCFS resources
still being used, and preventing WCFS from being unmounted cleanly.

-> Add cyclic GC support to PyBigFile / PyBigFileH

NOTE: we still don't allow PyVMA <=> PyBigFileH cycles to be collected,
because fileh_close called from fileh.__del__ asserts that there are no
live mappings left. See added comments for details. There is no
known practical need to use such cycles, so this should be ok.

See also other patches on cyclic GC topic:

- 450ad804 (bigarray: ArrayRef support for BigArray)  // adds cyclic GC support for PyVMA
- d97641d2 (bigfile/py: Properly untrack PyVMA from GC before dealloc)

/proposed-for-review-on nexedi/wendelin.core!12

The logic in pyvma_traverse and pyvma_clear needs to be synchronized
with PyVMA deallocation. In the next patche we'll be amending this
logic, and it will help a reader to keep all those functions together.

For the reference: PyVMA support for cyclic GC was introduced in
450ad804 (bigarray: ArrayRef support for BigArray). See also d97641d2
(bigfile/py: Properly untrack PyVMA from GC before dealloc).

/proposed-for-review-on !12