Handle ConnectionError before checking status_code

[arite]

In the event of a ConnectionError, when checking err.response.status_code an Uncaught Exception is thrown as the request object doesn't exist.

This occurs when the network is not fully ready. In my case this happens when running Mopidy as a daemon on startup (on a Raspberry Pi 2).

Example error:

2015-04-25 18:56:51,341 ERROR [226:MainThread] mopidy.commands: Uncaught exception
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/mopidy/commands.py", line 274, in run
    backends = self.start_backends(config, backend_classes, audio)
  File "/usr/lib/python2.7/dist-packages/mopidy/commands.py", line 352, in start_backends
    config=config, audio=audio).proxy()
  File "/usr/lib/python2.7/dist-packages/pykka/actor.py", line 93, in start
    obj = cls(*args, **kwargs)
  File "/usr/share/mopidy/mopidy_soundcloud/actor.py", line 21, in __init__
    self.remote = SoundCloudClient(config['soundcloud'])
  File "/usr/share/mopidy/mopidy_soundcloud/soundcloud.py", line 80, in __init__
    if err.response.status_code == 401:
AttributeError: 'NoneType' object has no attribute 'status_code'

By handling this exception first it prevents Mobidy from exiting prematurely.

[jodal]

Fixed by #61.