Improve Cinder Backup support

In my last commit on Cinder module, I add cinder::backup::swift
without adding cinder::backup class which is useful to ensure that
package is installed and service is running.
It also includes variables related to backup configuration.

Note: swift is one of the drivers of backup in Cinder, other ones should
be included in manifests/backup/<driver>.pp

Change-Id: I1a55245abe61f9bbd71568d76ed00e0ecf08307e
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>