Use a back-compat struct to handle listing volumes for volumes we know
about (because, presumably, they are being used by a container) for
volume drivers which don't yet support `List`.
Adds a fall-back for the volume driver `Get` call, which will use
`Create` when the driver returns a `404` for `Get`. The old behavior was
to always use `Create` to get a volume reference.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
