[FLOC-965] Acceptance testing against racksapce.

This is based on #1010. The relative diff is [here](https://github.com/ClusterHQ/flocker/compare/acceptance-runner-FLOC-1070...rackspace-acceptance-FLOC-965).

The linking tests fail due to [FLOC-1084](https://clusterhq.atlassian.net/browse/FLOC-1084).


I think that's reasonable.  I wonder what the benefit of doing this using fabric as a bunch of discrete actions is, though.  Couldn't this just be one shell script that gets dumped onto the node and executed in one go?

It looks like `_task_install_flocker` is probably the primary motivation for using Fabric here - there's actually some Python logic that controls what commands get executed.  Perhaps that logic wouldn't be any more complicated if it were working towards constructing commands to execute over an SSH connection without using Fabric?

I don't want to just say "don't use Fabric" here but if there's an outcome that results in similarly maintainable code that doesn't use Fabric I'd like to push in that direction. :smile: