In particular, do not flush all debug logs still in memory

- catch OperationFailure
- reset transaction manager when leaving backup mode
- send appropriate target tid to a storage that updates a outdated cell
- clean up partition table when leaving BACKINGUP state unexpectedly
- make sure all readable cells of a partition have the same 'backup_tid'
  if they have the same data, so that we know when internal replication is
  finished when leaving backup mode
- fix storage not finished internal replication when leaving backup mode

Found by pylint.

This fixes the following error:

PACKET #0x0012 AnswerTruncate                 > M1 (127.0.0.3:1)
ERROR  Pre-mortem data:
ERROR  Traceback (most recent call last):
ERROR    File "neo/storage/app.py", line 166, in run
ERROR      self._run()
ERROR    File "neo/storage/app.py", line 207, in _run
ERROR      self.doOperation()
ERROR    File "neo/storage/app.py", line 308, in doOperation
ERROR      task_queue[-1].next()
ERROR    File "neo/storage/handlers/storage.py", line 240, in push
ERROR      conn.notify(Packets.AddObject(oid, serial, *object[2:]))
ERROR  TypeError: 'bool' object is unsubscriptable

This fixes a regression in commit ad01f379
("fix leaving backup mode, including truncating to consistent TID")

Without this, transactions and even objects may be missing on the backup
database.