Dockerclient list volumes 289

Fixes #289 

In `flocker.node._deploy` the function `find_volume_changes` still needs to be updated where it currently performs comparison on volume names rather than the `AttachedVolume` object, but I suspect those changes should be done in a different branch, as the changes there will be quite substantial.
Don't want the backticks around the middle bit in the `:param`, it's a reference to a Python object.