Add support for swift volume backups

Gerrit topic: https://review.openstack.org/#q,topic:bp/volume-backups,n,z

Addressed by: https://review.openstack.org/53173
    Adding support for volume backups

[jpretorius 2013/12/03]
Note that cinder volume backups are not only swift any more, but now include RBD and TSM support. Ref: http://docs.openstack.org/havana/config-reference/content/section_backup-drivers.html

[david-lyle 2014-01-17] moving to i-3, needs more work.

[david-lyle 2014-02-28] this needs a rebase and rework based on other changes merged, won't be ready for icehouse.

[amotoki 2014-06-07] The review was abandoned. I hope the work is resumed. If you don't have time to work, I can volunteer to land the patch.

[jpichon 2014-06-10] Not sure what is the status for this, I noticed the owner has changed over to Matthew but there doesn't seem to be a new patch? I'll set the status back to "Started" for now.

[gary-smith 2014-06-10] Neither this blueprint for the patch mentions deleting backups, which is an
integral part of supporting volume backups. Can that be included in this blueprint (given its title), or
should a new one be created?

[lin-hua-cheng 2014-06-11] Talked to Matt, I'll take over fixing the comments.

The existing patch already includes delete backup

Backup is an optional configuration in cinder, there is no way to determine if it is configured. Ticket opened to expose that capability: https://bugs.launchpad.net/cinder/+bug/1334856

Addressed by: https://review.openstack.org/104303
    Adding support for volume backups