Using correct volume driver paths

  cinder.volume.X instead of cinder.volume.drivers.X results in a
  deprecation warning in the cinder-volume log.

  https://github.com/openstack/cinder/blob/master/etc/cinder/cinder.conf.sample#L1352-L1353

Change-Id: Ica4ff79b3ccc35a9d3ff64bdc0bb89a94e7ead1f
Merge "Using correct volume driver paths"