Move responsibility of ls/inspect to volume driver

Makes `docker volume ls` and `docker volume inspect` ask the volume
drivers rather than only using what is cached locally.

Previously in order to use a volume from an external driver, one would
either have to use `docker volume create` or have a container that is
already using that volume for it to be visible to the other volume
API's.

For keeping uniqueness of volume names in the daemon, names are bound to
a driver on a first come first serve basis. If two drivers have a volume
with the same name, the first one is chosen, and a warning is logged
about the second one.

Adds 2 new methods to the plugin API, `List` and `Get`.
If a plugin does not implement these endpoints, a user will not be able
to find the specified volumes as well requests go through the drivers.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

daemon/create_unix.go

@@ -51,7 +51,7 @@ func (daemon *Daemon) createContainerPlatformSpecificSettings(container *contain
 			}
 		}
 
-		v, err := daemon.createVolume(name, volumeDriver, nil)
+		v, err := daemon.volumes.CreateWithRef(name, volumeDriver, container.ID, nil)
 		if err != nil {
 			return err
 		}