Add auth_plugin support to cinderclient

With CINDER_RAX_AUTH being rightfully removed, cinderclient is no longer
compatible with Rackspace/any non-keystone auth. To fix this, I stole
auth_system/auth_plugin from novaclient's implementation.

See https://review.openstack.org/#/c/23820/.

Change-Id: If5f84003f868ef02bb7eb7da67cf62018602e8f0
Closes-Bug: 1280393
Accept deleting multiple snapshots in one shot

In bug 1241941 the delete and force-delete commands were updated to
accept multiple volumes for deleting in the same call. This patch adds
the same behaviour to the snapshot-delete command.

Closes-Bug: #1284540
Change-Id: I5e4bf8641d7fd261fa24b03832bad08007e43c12
Fix malformed encryption-type body in test cases

This change addresses bug #1286261 and fixes two malformed
encryption-type bodies in two test_create test cases.

Change-Id: I308561c1d5a70812889a93922e13194597f670f1
Closes-Bug: #1286261
Merge "Add auth_plugin support to cinderclient"
Merge "Accept deleting multiple snapshots in one shot"