Automatic IP address detection messed up by VPN

[n8henrie]

@candrews67 emailed me to note that Fauxmo wasn't working. He uses a VPN address and found that it would work sometimes depending on the status of the VPN. Here's his traceback:

Traceback (most recent call last):
  File "fauxmo/venv/bin/fauxmo", line 9, in <module>
    load_entry_point('fauxmo==0.1.7', 'console_scripts', 'fauxmo')()
  File "fauxmo/fauxmo/cli.py", line 37, in cli
    main(config_path=args.config, verbosity=verbosity)
  File "fauxmo/fauxmo/fauxmo.py", line 166, in main
    action_handler=action_handler)
  File "fauxmo/fauxmo/fauxmo.py", line 53, in __init__
    ip_address=self.ip_address)
  File "fauxmo/fauxmo/upnp.py", line 75, in __init__
    self.socket.bind((self.ip_address, self.port))
OSError: [Errno 49] Can't assign requested address

With some tinkering, I think we figured out that it's a problem with the get_local_ip function in upnp.py, and it works with a manually specified IP address. In cases like this, it would be nice if there was a way to override the automatic IP detection.