More intelligent error handling if unable to find redis DB

[will-hart]

In serial line 74, Currently just fails to create the DB manager and then just errors every time it tries to do something with the data manager

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• Bitbucket: https://bitbucket.org/willhart/blitz_gui/issue/18
• Originally Reported By: Will Hart
• Originally Created At: 2013-07-06T02:37:16.423

[will-hart]

Currently logs critical errors but doesn't then do anything about it. The client then continues as normal but doesn't receive intelligent responses from the server.

[will-hart]

Related stack trace on the server:

Traceback (most recent call last):
  File "C:\Python27\lib\threading.py", line 551, in __bootstrap_inner
    self.run()
  File "C:\Python27\lib\threading.py", line 504, in run
    self.__target(*self.__args, **self.__kwargs)
  File "C:\Users\mecharius\Dropbox\blitz\blitz\communications\tcp.py", line 248, in run
    self.__current_state = self.__current_state.receive_message(self.__tcp, request.command)
  File "C:\Users\mecharius\Dropbox\blitz\blitz\communications\server_states.py", line 107, in receive_message
    sigs.server_status_request.send(tcp)
  File "C:\Python27\lib\site-packages\blinker\base.py", line 267, in send
    for receiver in self.receivers_for(sender)]
  File "C:\Users\mecharius\Dropbox\blitz\blitz\server.py", line 186, in serve_client_status
    message = self.serial_server.database.get_latest_from_session(self.serial_server.database.session_id)
AttributeError: 'NoneType' object has no attribute 'get_latest_from_session'

[will-hart]

This will rely on the server plugin refactoring (#51) which will bring the database class out into the server proper. Suggested implementation is to create a ServerErrorState TCP state which returns an error code in response to all transmissions.

For a database error no data acquisition is possible so we don't the client to do anything until this is fixed.