Introduce an option for users to bind-mount Cinder volumes to
containers. The syntax will look like:
$ zun run --mount source=my-volume,destination=/data <image>
The above command will bind-mount cinder volume with name 'my-volume'
into path '/data' inside the container.
Change-Id: If8e44527e65cf574400b9043108e75b473b3627c
Partial-Implements: blueprint direct-cinder-integration