Flocker deploy 121

I would like this to be looked over by someone, for guidance on what needs to be done, and confirmation I'm on the right track.

And, now, the comment on #121 that some of this might not be necessary for now.

There are a couple of inline "TODO"s I'm not sure about.

Fixes #121 
`run_expecting_error` isn't actually used and the `run` function hardly seems worth using. Just call `check_output` directly in the test. 
That'll be enough to demonstrate that this command has been installed on the system path. The unit tests cover the rest.
I'm not sure if the `flocker-volume` command is going to be fully implemented but if it is, then the functional tests for all commands might be moved to this module.