Tempest for revert-to-snapshot

Added tempest testcases for revert-to-snapshot feature.

Depends-On: 16518c3b293561a2e9f4fa42a5247345ebd1e2b3
Change-Id: I97a9241ce53b144c30bc16d65dc8cf6e3f679743
diff --git a/cinder/tests/tempest/cinder_clients.py b/cinder/tests/tempest/cinder_clients.py
index 8f829ef..aad32d4 100644
--- a/cinder/tests/tempest/cinder_clients.py
+++ b/cinder/tests/tempest/cinder_clients.py
@@ -16,6 +16,7 @@
 from tempest import config
 
 from cinder.tests.tempest.services import consistencygroups_client
+from cinder.tests.tempest.services import volume_revert_client
 
 CONF = config.CONF
 
@@ -35,3 +36,5 @@
         self.consistencygroups_adm_client = (
             consistencygroups_client.ConsistencyGroupsClient(auth_provider,
                                                              **params))
+        self.volume_revet_client = (
+            volume_revert_client.VolumeRevertClient(auth_provider, **params))