Add Swift as backup backend support

Cinder can backup volumes in different backends.
Swift will be the first one supported by puppet-cinder.

New class: cinder::backup::swift

Change-Id: Iec0a48681da8fd987955cabae49d411ede1e255e
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
(cherry picked from commit f0b2f7daa7205b3f709063fded713a4cb6b7d0db)
Merge "Add Swift as backup backend support" into stable/havana