Don't try to send self address when connecting as read-only
Don't try to send self address when connecting as read-only

When connecting as readonly node to the cluster with encryption enabled
the _onOutgoingMessageReceived() method tried to unconditionally send
_selfNode.address after an exchange of random keys. Since the
_selfNode.address is None following exception was raised:
```python
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "/usr/lib/python2.7/threading.py", line 754, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/local/lib/python2.7/dist-packages/pysyncobj/syncobj.py", line 505, in _autoTickThread
    self._onTick(self.__conf.autoTickPeriod)
  File "/usr/local/lib/python2.7/dist-packages/pysyncobj/syncobj.py", line 617, in _onTick
    self._poller.poll(timeToWait)
  File "/usr/local/lib/python2.7/dist-packages/pysyncobj/poller.py", line 97, in poll
    self.__descrToCallbacks[descr](descr, eventMask)
  File "/usr/local/lib/python2.7/dist-packages/pysyncobj/tcp_connection.py", line 174, in __processConnection
    self.__onMessageReceived(message)
  File "/usr/local/lib/python2.7/dist-packages/pysyncobj/transport.py", line 455, in _onOutgoingMessageReceived
    conn.send(self._selfNode.address)
AttributeError: 'NoneType' object has no attribute 'address'
```

bakwc/PySyncObj