Reportstate 11

Provisionally fixes #11
Opening PR with the expectation that there is probably a bit more stuff to do, but some comments would be appreciated.
Current output of `[vagrant@localhost flocker]$ flocker-reportstate --config=/home/vagrant/test1.json` is:

`main function encountered error
Traceback (most recent call last):
Failure: twisted.internet.defer.FirstError: FirstError[#1, [Failure instance: Traceback (failure with no frames): <class 'flocker.volume.filesystems.zfs.CommandFailed'>:
]]
Unhandled error in Deferred:
Unhandled Error
Traceback (most recent call last):
Failure: flocker.volume.filesystems.zfs.CommandFailed:`