Push volumes from one node to another (fixes 16, 90)

This fixes #16, and also #90 so that the tests run on Buildbot.
It's only there for testing, yeah. The problem with the functional tests is you ssh to remote node and it's trying to use global config for `flocker-volume`, that's not so great... In general the testing issues are pretty terrible, thus #125 which hopefully will deal with this too.

In a non-ssh based API you'd just run the server you were connecting to with appropriate configuration, so this isn't the end of the world.