It is often faster to set up replicas by stopping a node (and any
underlying database server like MariaDB) and do a raw copy of the
database (e.g. with rsync). So far, it required to stop the whole
cluster and use tools like 'mysql' or sqlite3' to edit:
- the 'pt' table in databases,
- the 'config.nid' values of the new nodes.

With this new option, if you already have 1 replica, you can set up
new replicas with such fast raw copy, and without interruption of
service. Obviously, this implies less redundancy during the operation.

--kill-mysqld should be combined with something like -f .3 -r .1
to give storage nodes enough time to recover.
And also -D 0 to focus testing on the storage backend rather than NEO.

This also reverts commit 442bb43a.

This fixes up commit be839e92.

This is not used currently.

This breaks compatibily but it was mentionned from the beginning
that these options are only there for testing purpose.

TODO: rename all remaining occurrences of UUID into NID in the code

If the source DB is lost during the import and then restored from a backup,
all new transactions have to written back again on resume. It is the most
common case for which the writeback hits the maximum number of transactions
per partition to process at each iteration; the previous code was buggy in
that it could skip transactions.

Example output:

    stress: yes (toggle with F1)
    cluster state: RUNNING
    last oid: 0x44c0
    last tid: 0x3cdee272ef19355 (2019-02-26 15:35:11.002419)
    clients: 2308, 2311, 2302, 2173, 2226, 2215, 2306, 2255, 2314, 2356 (+48)
            8m53.988s (42.633861/s)
    pt id: 4107
        RRRDDRRR
     0: OU......
     1: ..UO....
     2: ....OU..
     3: ......UU
     4: OU......
     5: ..UO....
     6: ....OU..
     7: ......UU
     8: OU......
     9: ..UO....
    10: ....OU..
    11: ......UU
    12: OU......
    13: ..UO....
    14: ....OU..
    15: ......UU
    16: OU......
    17: ..UO....
    18: ....OU..
    19: ......UU
    20: OU......
    21: ..UO....
    22: ....OU..
    23: ......UU

getAddress (via __repr__) raised EBADF on closed connectors.

In functional tests (or anything reusing this framework),
the mapping could be incorrect at the beginning of logs.

Corrupted logs cause neolog to fail with the following error:

  AttributeError: 'Log' object has no attribute 'uuid_str'

This makes commit 3c7a3160
(storage: speed up reads by indexing 'obj' primarily by 'oid')
effective for SQLite.

The fake changes in test data are because we don't force upgrade
for this optimization.

Commit aa4d621d broke log rotation
and neolog sometimes failed to read in new format.

neolog has new options: -N for old behaviour, and -C to show the cluster name.

Since commit 50e7fe52,
some code can be simplified.

This fixes a bug that could manifest as follows:

  Traceback (most recent call last):
    File "neo/client/app.py", line 432, in load
      self._cache.store(oid, data, tid, next_tid)
    File "neo/client/cache.py", line 223, in store
      assert item.tid == tid, (item, tid)
  AssertionError: (<CacheItem oid='\x00\x00\x00\x00\x00\x00\x00\x01' tid='\x03\xcb\xc6\xca\xfd\xc7\xda\xee' next_tid='\x03\xcb\xc6\xca\xfd\xd8\t\x88' data='...' counter=1 level=1 expire=10000 prev=<...> next=<...>>, '\x03\xcb\xc6\xca\xfd\xd8\t\x88')

The big changes in the threaded test framework are required because we need to
reproduce a race condition between client threads and this conflicts with the
serialization of epoll events (deadlock).

This was found when stress-testing a big cluster. 1 client node was stuck:

  (Pdb) pp app.dispatcher.__dict__
  {'lock_acquire': <built-in method acquire of thread.lock object at 0x7f788c6e4250>,
  'lock_release': <built-in method release of thread.lock object at 0x7f788c6e4250>,
  'message_table': {140155667614608: {},
                    140155668875280: {},
                    140155671145872: {},
                    140155672381008: {},
                    140155672381136: {},
                    140155672381456: {},
                    140155673002448: {},
                    140155673449680: {},
                    140155676093648: {170: <neo.lib.locking.SimpleQueue object at 0x7f788a109c58>},
                    140155677536464: {},
                    140155679224336: {},
                    140155679876496: {},
                    140155680702992: {},
                    140155681851920: {},
                    140155681852624: {},
                    140155682773584: {},
                    140155685988880: {},
                    140155693061328: {},
                    140155693062224: {},
                    140155693074960: {},
                    140155696334736: {278: <neo.lib.locking.SimpleQueue object at 0x7f788a109c58>},
                    140155696411408: {},
                    140155696414160: {},
                    140155696576208: {},
                    140155722373904: {}},
  'queue_dict': {140155673622936: 1, 140155689147480: 2}}

140155673622936 should not be queue_dict

The idea is to write:

  with self.expectedFailure(...): \

just before the statement that is expected to fail. Contrary to the existing
decorator, we want to:
- be sure that the test fails at the expected line;
- be able to remove an expectedFailure without touching the code around.