Add Ceph as backup backend support

Cinder backup could use Ceph as backend.
This patch aims to create cinder::backup::ceph class to use this driver.

Change-Id: Ib82b94f3e2d5d9e2287a570a435d469656c9a756
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Merge "Add Ceph as backup backend support"