* master:
  storage: fix crash when a client loses connection to the master just before voting
  no change: only some code reindentation
  Enable branch coverage measurement by default
  coverage: add support for functional tests

This is similar to commit 7aecdada
and for completeness, we also protect unlock the same way.

For 2 previous commits, we didn't reindent in order to keep the diff readable.

See 9385706f (Fix identification issues, including a race condition
causing id conflicts).

The added test describes how the new id timestamps fix the race condition.
These timestamps could be any unique opaque values, and the protocol is
extended to exchange them along with node ids.

Internally, nodes also reuse timestamps as a marker to identify the first
NotifyNodeInformation packets from the master: since this packet is a complete
list of nodes in the cluster, any other node in the node manager has left the
cluster definitely and is removed.

The secondary masters didn't receive update about master nodes.
It's also useless to send them information about non-master nodes.

When Client (including backup master) and admin nodes are identified,
the primary master now sends them automatically all nodes with
NotifyNodeInformation, as with storage nodes.

- check address conflicts
- on invalid values, reject peer instead of dying

Listing connected/connecting nodes with a UUID is used:
- in one place by storage nodes: here, it does not matter if we skip nodes that
  aren't really identified
- in many places by the master, only for server connections, in which case we
  have equivalence with real identification

So in practice, NodeManager is only simplified to reuse the 'identified'
property of nodes.

Therefore, a client node in the node manager is always RUNNING.

Although the change applies to any node with a temporary ids (all but storage),
only clients don't have addresses and are therefore not recognizable.

After a client is disconnected from the master and before reconnecting, another
client may join the cluster and "steals" the id of the first client. This issue
leads to stuck clients, failing in loop with exceptions like the following one:

    ERROR ZODB.Connection Couldn't load state for 0x0251
    Traceback (most recent call last):
      File "ZODB/Connection.py", line 860, in setstate
        self._setstate(obj)
      File "ZODB/Connection.py", line 901, in _setstate
        p, serial = self._storage.load(obj._p_oid, '')
      File "neo/client/Storage.py", line 82, in load
        return self.app.load(oid)[:2]
      File "neo/client/app.py", line 353, in load
        data, tid, next_tid, _ = self._loadFromStorage(oid, tid, before_tid)
      File "neo/client/app.py", line 373, in _loadFromStorage
        for node, conn in self.cp.iterateForObject(oid, readable=True):
      File "neo/client/pool.py", line 91, in iterateForObject
        pt = self.app.pt
      File "neo/client/app.py", line 145, in __getattr__
        self._getMasterConnection()
      File "neo/client/app.py", line 214, in _getMasterConnection
        result = self.master_conn = self._connectToPrimaryNode()
      File "neo/client/app.py", line 246, in _connectToPrimaryNode
        handler=handler)
      File "neo/lib/threaded_app.py", line 154, in _ask
        _handlePacket(qconn, qpacket, kw, handler)
      File "neo/lib/threaded_app.py", line 135, in _handlePacket
        handler.dispatch(conn, packet, kw)
      File "neo/lib/handler.py", line 66, in dispatch
        method(conn, *args, **kw)
      File "neo/lib/handler.py", line 188, in error
        getattr(self, Errors[code])(conn, message)
      File "neo/client/handlers/__init__.py", line 23, in protocolError
        raise StorageError("protocol error: %s" % message)
    StorageError: protocol error: already connected

* master:
  coverage: CacheItem.__repr__ (client)
  New neotestrunner option for code coverage testing

* x/go:
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  X notes on partition table
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* master:
  client: fix item eviction from cache, which could break loading from storage
  Bump protocol version for new read-only mode in BACKUPING state
  backup: Teach cluster in BACKUPING state to also serve regular ZODB clients in read-only mode
  tests/threaded: Add handy shortcuts to NEOCluster to concisely check cluster properties in tests