Added Cinder volume backup to Ceph support

Added new Ceph backup service to allow backup
of Cinder volumes to a Ceph object store. This
driver is compatible with the existing backup
interface provided by the Swift backup service.

Also added backup and restore to RBD driver.

Change-Id: Id0931e308fd3c15ec3901e8e666c19decec09b41
Implements: blueprint cinder-backup-to-ceph