cinder: use non-deprecated notification_driver

Cinder has been using oslo.messaging since Icehouse so it should be
using 'messaging' as its notification driver and not the now deprecated
full python path to the oslo-incubator notification driver.

Change-Id: I3edca1ff54e51b464cc1b23935c8530e2e242fee
Merge "cinder: use non-deprecated notification_driver"
Merge commit 'refs/changes/83/86083/2' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch