Adds support for container selection for backup

Changed argument from parsed_args.volume to parsed_args.container as per what
is expected in python-cinderclient.

If not defined, defaults to "backup_swift_container" in cinder.conf.

Stops there being a container for every volume you take backups off.

Change-Id: I4a34894222f71b0f207d007c32427040589406aa
Closes-Bug: 1446751

Author: stenstad

openstackclient/volume/v1/backup.py

@@ -64,7 +64,7 @@ def take_action(self, parsed_args):
                                         parsed_args.volume).id
         backup = volume_client.backups.create(
             volume_id,
-            parsed_args.volume,
+            parsed_args.container,
             parsed_args.name,
             parsed_args.description
         )