Allow login timeout to be variable #207

Currently for SSH connections Trigger defaults to the Twisted default login timeout of 30 seconds.

This is configurable when calling reactor.connectTCP() on a new client connection by pasing timeout=n (where setting timeout=None disables timeout). We are not currently setting the timeout value.

Currently the timeout= argument supported by Commando, NetDevice.execute() only sets the timeout for executing commands.

This will be a good enhancement to allow for distinction between command timeouts (e.g. command_timeout=) and login timeouts (e.g. login_timeout=) settings both globally in settings.py and on NetDevice.connect() calls, on NetDevice.execute() calls and on Commando subclasses.

FYI @johnfzc