fsnotify uses unsafe and we are digging GC crash trying to avoid Cgo and
unsafe.

For example NEOCluster needs to shutdown gracefully, else there are
processes left for e.g. storage nodes and they dump somthing as below on
the terminal after tests completion:

    === RUN   TestLoad
    2020/10/21 14:33:00 zodb: FIXME: open ../zodb/storage/fs1/testdata/1.fs: raw cache is not ready for invalidations -> NoCache forced
    === RUN   TestLoad/py
    I: runneo.py: /tmp/neo445013868/1: Started master(s): 127.0.0.1:24661
    WARNING: This is not the recommended way to import data to NEO: you should use the Importer backend instead.
    NEO also does not implement IStorageRestoreable interface, which means that undo information is not preserved when using this tool: conflict resolution could happen when undoing an old transaction.
    Migrating from ../zodb/storage/fs1/testdata/1.fs to 127.0.0.1:24661
    Migration done in 0.19877
    --- PASS: TestLoad (0.75s)
        --- PASS: TestLoad/py (0.74s)
    PASS
    ok      lab.nexedi.com/kirr/neo/go/neo  0.749s
    (neo) (z-dev) (g.env) kirr@deco:~/src/neo/src/lab.nexedi.com/kirr/neo/go/neo$ Traceback (most recent call last):
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/tests/functional/__init__.py", line 182, in start
        getattr(neo.scripts,  command).main()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/scripts/neostorage.py", line 66, in main
        app.run()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/storage/app.py", line 147, in run
        self._run()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/storage/app.py", line 178, in _run
        self.doOperation()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/storage/app.py", line 266, in doOperation
        poll()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/storage/app.py", line 87, in _poll
        self.em.poll(1)
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/lib/event.py", line 155, in poll
        self._poll(blocking)
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/lib/event.py", line 253, in _poll
        timeout_object.onTimeout()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/lib/event.py", line 259, in onTimeout
        on_timeout()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/storage/database/manager.py", line 207, in _deferredCommit
        self.commit()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/storage/database/manager.py", line 193, in commit
        self._commit()
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/storage/database/sqlite.py", line 90, in _commit
        retry_if_locked(self.conn.commit)
      File "/home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/neo/storage/database/sqlite.py", line 45, in retry_if_locked
        return f(*args)
    OperationalError: disk I/O error

This fixes

	=== RUN   TestLoad/py
	    xtesting.go:297: load 0285cbacc06d3a4c:0000000000000007: returned err unexpected:
	        have: <nil>
	        want: neo://1@127.0.0.1:27145: load 0285cbacc06d3a4c:0000000000000007: 0000000000000007: object was deleted @0285cbacc06d3a4c
	    xtesting.go:297: load 0285cbacc06d3a4c:0000000000000007: returned tid unexpected: 0285cbacc06d3a4c  ; want: 0285cbacc06d3a4c
	    xtesting.go:297: load 0285cbacc06d3a4c:0000000000000007: returned buf != nil
	    xtesting.go:297: load 0285cbad858bf2e6:0000000000000006: returned err unexpected:
	        have: <nil>
	        want: neo://1@127.0.0.1:27145: load 0285cbad858bf2e6:0000000000000006: 0000000000000006: object was deleted @0285cbad858bf2e6
	    xtesting.go:297: load 0285cbad858bf2e6:0000000000000006: returned tid unexpected: 0285cbad858bf2e6  ; want: 0285cbad858bf2e6
	    xtesting.go:297: load 0285cbad858bf2e6:0000000000000006: returned buf != nil
	    xtesting.go:315: load 7fffffffffffffff:0000000000000006: returned err unexpected:
	        have: <nil>
	        want: neo://1@127.0.0.1:27145: load 7fffffffffffffff:0000000000000006: 0000000000000006: object was deleted @0285cbad858bf2e6
	    xtesting.go:315: load 7fffffffffffffff:0000000000000006: returned tid unexpected: 0285cbad858bf2e6  ; want: 0285cbad858bf2e6
	    xtesting.go:315: load 7fffffffffffffff:0000000000000006: returned buf != nil
	    xtesting.go:315: load 7fffffffffffffff:0000000000000007: returned err unexpected:
	        have: <nil>
	        want: neo://1@127.0.0.1:27145: load 7fffffffffffffff:0000000000000007: 0000000000000007: object was deleted @0285cbacc06d3a4c
	    xtesting.go:315: load 7fffffffffffffff:0000000000000007: returned tid unexpected: 0285cbacc06d3a4c  ; want: 0285cbacc06d3a4c
	    xtesting.go:315: load 7fffffffffffffff:0000000000000007: returned buf != nil

NEO/py sends all zeros for empty data. Without this fix tests fail:

    --- FAIL: TestLoad/py (0.74s)
        xtesting.go:297: load 0285cbacc06d3a4c:0000000000000007: returned err unexpected:
            have: neo://1@127.0.0.1:25910: load 0285cbacc06d3a4c:0000000000000007: data corrupt: checksum mismatch
            want: neo://1@127.0.0.1:25910: load 0285cbacc06d3a4c:0000000000000007: 0000000000000007: object was deleted @0285cbacc06d3a4c
        xtesting.go:297: load 0285cbad858bf2e6:0000000000000006: returned err unexpected:
            have: neo://1@127.0.0.1:25910: load 0285cbad858bf2e6:0000000000000006: data corrupt: checksum mismatch
            want: neo://1@127.0.0.1:25910: load 0285cbad858bf2e6:0000000000000006: 0000000000000006: object was deleted @0285cbad858bf2e6
        xtesting.go:315: load 7fffffffffffffff:0000000000000006: returned err unexpected:
            have: neo://1@127.0.0.1:25910: load 7fffffffffffffff:0000000000000006: data corrupt: checksum mismatch
            want: neo://1@127.0.0.1:25910: load 7fffffffffffffff:0000000000000006: 0000000000000006: object was deleted @0285cbad858bf2e6
        xtesting.go:315: load 7fffffffffffffff:0000000000000007: returned err unexpected:
            have: neo://1@127.0.0.1:25910: load 7fffffffffffffff:0000000000000007: data corrupt: checksum mismatch
            want: neo://1@127.0.0.1:25910: load 7fffffffffffffff:0000000000000007: 0000000000000007: object was deleted @0285cbacc06d3a4c

* master:
  go/zodb/zeo: Skip handshake/py/msgpack=true on ZEO4

ZEO4 does not have msgpack support and does not take $ZEO_MSGPACK into
account. With ZEO4 this test was failing before:

	--- FAIL: TestHandshake (0.46s)
	    --- FAIL: TestHandshake/py/msgpack=true (0.24s)
	        zeo_test.go:241: handshake: encoding=Z  ; want M

We don't have infrastructure to check python packages versions, so
check it by verifying ZEO.asyncio presence.

In the Importer storage backend, the repickler code never really worked with
ZODB 5 (use of protocol > 1), and now the test does not pass anymore.

The other issues caused by ZODB commit 12ee41c47310156027a674932df34b60de86ba36
are fixed:

  TypeError: list indices must be integers, not binary

  ValueError: unsupported pickle protocol: 3

Although not necessary as long as we don't support Python 3,
this commit also replaces `str` by `bytes` in a few places.

* master:
  go/zodb/zeo: Fix initialization when server database is empty
  neotest: info-local: Fix NIC display for virtio devices
  neotest: info-local: Fix it when CPU frequence/idle information is not available

In that case at0 was initialized as 0 and still considered uninitialized
by flushEventq0:

    (neo) (z-dev) (g.env) kirr@deco:~/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo$ go test -run Empty
    ------
    2020-10-12T07:39:25 INFO ZEO.runzeo (146240) opening storage '1' using FileStorage
    ------
    2020-10-12T07:39:25 INFO ZEO.StorageServer StorageServer created RW with storages: 1:RW:/tmp/zeo905263273/1.fs
    ------
    2020-10-12T07:39:25 INFO ZEO.asyncio.server listening on /tmp/zeo905263273/1.fs.zeosock
    ------
    2020-10-12T07:39:25 INFO ZEO.asyncio.base Connected server protocol
    ------
    2020-10-12T07:39:25 INFO ZEO.asyncio.server received handshake 'Z5'
    2020/10/12 07:39:25 /tmp/zeo905263273/1.fs.zeosock: EOF
    --- FAIL: TestEmptyDB (0.22s)
        --- FAIL: TestEmptyDB/py/msgpack=false (0.22s)
    panic: flush, but .at0 not yet initialized [recovered]
            panic: flush, but .at0 not yet initialized

    goroutine 7 [running]:
    testing.tRunner.func1.1(0x644a60, 0x6e1a50)
            /home/kirr/src/tools/go/go/src/testing/testing.go:1072 +0x30d
    testing.tRunner.func1(0xc000001e00)
            /home/kirr/src/tools/go/go/src/testing/testing.go:1075 +0x41a
    panic(0x644a60, 0x6e1a50)
            /home/kirr/src/tools/go/go/src/runtime/panic.go:969 +0x175
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.(*zeo).flushEventq0(0xc00018a000)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo.go:180 +0xf3
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.openByURL(0x6e9ca0, 0xc000016108, 0xc000138120, 0xc000153d98, 0x0, 0x0, 0x0, 0x0, 0x0)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo.go:488 +0x5ba
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.zeoOpen(0xc000018740, 0x1e, 0xc000049d98, 0x0, 0x0, 0x0, 0x0)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo_test.go:285 +0x17b
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.withZEO.func1(0xc000001e00, 0x6e9ea0, 0xc00005e6c0)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo_test.go:219 +0xd0
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.withZEOSrv.func2.1(0xc0000185c0, 0x16)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo_test.go:205 +0xfb
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.withZEOSrv.func1(0xc000001e00, 0xc00000e5a0)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo_test.go:185 +0x129
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.withZEOSrv.func2(0xc000001e00)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo_test.go:197 +0x105
    testing.tRunner(0xc000001e00, 0xc00000e440)
            /home/kirr/src/tools/go/go/src/testing/testing.go:1123 +0xef
    created by testing.(*T).Run
            /home/kirr/src/tools/go/go/src/testing/testing.go:1168 +0x2b3
    exit status 2
    FAIL    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo     0.227s

-> Fix it by using dedicated field marking whether .at0 was initialized or not yet.

In that case at0 was initialized as 0 and still considered uninitialized
by flushEventq0:

    (neo) (z-dev) (g.env) kirr@deco:~/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo$ go test -run Empty
    ------
    2020-10-12T07:39:25 INFO ZEO.runzeo (146240) opening storage '1' using FileStorage
    ------
    2020-10-12T07:39:25 INFO ZEO.StorageServer StorageServer created RW with storages: 1:RW:/tmp/zeo905263273/1.fs
    ------
    2020-10-12T07:39:25 INFO ZEO.asyncio.server listening on /tmp/zeo905263273/1.fs.zeosock
    ------
    2020-10-12T07:39:25 INFO ZEO.asyncio.base Connected server protocol
    ------
    2020-10-12T07:39:25 INFO ZEO.asyncio.server received handshake 'Z5'
    2020/10/12 07:39:25 /tmp/zeo905263273/1.fs.zeosock: EOF
    --- FAIL: TestEmptyDB (0.22s)
        --- FAIL: TestEmptyDB/py/msgpack=false (0.22s)
    panic: flush, but .at0 not yet initialized [recovered]
            panic: flush, but .at0 not yet initialized

    goroutine 7 [running]:
    testing.tRunner.func1.1(0x644a60, 0x6e1a50)
            /home/kirr/src/tools/go/go/src/testing/testing.go:1072 +0x30d
    testing.tRunner.func1(0xc000001e00)
            /home/kirr/src/tools/go/go/src/testing/testing.go:1075 +0x41a
    panic(0x644a60, 0x6e1a50)
            /home/kirr/src/tools/go/go/src/runtime/panic.go:969 +0x175
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.(*zeo).flushEventq0(0xc00018a000)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo.go:180 +0xf3
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.openByURL(0x6e9ca0, 0xc000016108, 0xc000138120, 0xc000153d98, 0x0, 0x0, 0x0, 0x0, 0x0)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo.go:488 +0x5ba
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.zeoOpen(0xc000018740, 0x1e, 0xc000049d98, 0x0, 0x0, 0x0, 0x0)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo_test.go:285 +0x17b
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.withZEO.func1(0xc000001e00, 0x6e9ea0, 0xc00005e6c0)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo_test.go:219 +0xd0
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.withZEOSrv.func2.1(0xc0000185c0, 0x16)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo_test.go:205 +0xfb
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.withZEOSrv.func1(0xc000001e00, 0xc00000e5a0)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo_test.go:185 +0x129
    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo.withZEOSrv.func2(0xc000001e00)
            /home/kirr/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/storage/zeo/zeo_test.go:197 +0x105
    testing.tRunner(0xc000001e00, 0xc00000e440)
            /home/kirr/src/tools/go/go/src/testing/testing.go:1123 +0xef
    created by testing.(*T).Run
            /home/kirr/src/tools/go/go/src/testing/testing.go:1168 +0x2b3
    exit status 2
    FAIL    lab.nexedi.com/kirr/neo/go/zodb/storage/zeo     0.227s

-> Fix it by using dedicated field marking whether .at0 was initialized or not yet.