Before this, if a volume exists in a driver but not in the local cache,
the store would just return a bare volume. This means that if a user
supplied options or labels, they will not get stored.
Instead only return early if we have the volume stored locally. Note
this could still have an issue with labels/opts passed in by the user
differing from what is stored, however this isn't really a new problem.
This fixes a problem where if there is a shared storage backend between
two docker nodes, a create on one node will have labels stored and a
create on the other node will not.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>