Enable volume backup tests

As of commit I7e7dbdae72a08e663a96b6c01340ec2a5cbe883e , the gate
failure in cinder-backup tests should be fixed.
This patch checks for the same by unskipping the backup tests.

Change-Id: I1a2e80cbb3093aab3a3c21b2b761d3bb9aae86d9
diff --git a/tempest/api/volume/test_volumes_backup.py b/tempest/api/volume/test_volumes_backup.py
index 6ce5d3e..c178272 100644
--- a/tempest/api/volume/test_volumes_backup.py
+++ b/tempest/api/volume/test_volumes_backup.py
@@ -50,7 +50,6 @@
                                                 'available')
         return restored_volume
 
-    @decorators.skip_because(bug="1483434")
     @testtools.skipIf(CONF.volume.storage_protocol == 'ceph',
                       'ceph does not support arbitrary container names')
     @decorators.idempotent_id('a66eb488-8ee1-47d4-8e9f-575a095728c6')