Generic backup_volume and restore_backup functions

Add implementation for backup_volume and restore_backup to the
VolumeDriver class, which uses brick for attach and detach.
Add default NotImplmeneted implmentation for non block drivers:
remotefs, coraid, gpfs, scality, sheepdog and sm.

Change-Id: I291390a58608b14f0deea703fc5cec3e34b965cd
Merge "Generic backup_volume and restore_backup functions"