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.
We should try to make our error messages as consistent as possible. A similar error is "Non-ASCII hostname: {hostname}" in `flocker-changestate`. These should be the same (I don't have a preference).