[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).


Do names have to be unique on rackspace?  Either way it might be handy to identify the node in more detail than this.  I think Rackspace already keeps metadata like when the instance was started.  Maybe we could add to that - what host was running the acceptance tests that caused it to be started or what username was running the process or something.