Flocker deploy ssh config 71

Fixes #71 
You're discarding stdout and stderr when calling many of these subprocesses, but I'd have thought that there may be useful debug output in there in the event of a test failure.
Doesn't `trial` redirect `stdout` to `test.log` anyway. And therefore wouldn't it be better to redirect `stderr` to `stdout` so that all debug and error messages are logged.
If you disagree, maybe you'd add a comment to https://github.com/ClusterHQ/flocker/issues/171 about your preferred solution.