Port to the tempest stable plugin interface (clients)

This is one of the last tempest plugins which was still not using
the proper interface to define its clients.
(Hopefully) no behavioral changes, just refactoring.

Change-Id: Ia57c771186cd1bf283f30b58007395d33aefa4a9
diff --git a/cinder_tempest_plugin/cinder_clients.py b/cinder_tempest_plugin/cinder_clients.py
index f4c7c0e..b27d22c 100644
--- a/cinder_tempest_plugin/cinder_clients.py
+++ b/cinder_tempest_plugin/cinder_clients.py
@@ -14,27 +14,19 @@
 #    under the License.
 
 from tempest import config
-
-from cinder_tempest_plugin.services import consistencygroups_client
-from cinder_tempest_plugin.services import volume_revert_client
+from tempest.lib.services import clients
 
 CONF = config.CONF
 
 
-class Manager(object):
-    def __init__(self, base_manager):
-        params = {
-            'service': CONF.volume.catalog_type,
-            'region': CONF.volume.region or CONF.identity.region,
-            'endpoint_type': CONF.volume.endpoint_type,
-            'build_interval': CONF.volume.build_interval,
-            'build_timeout': CONF.volume.build_timeout
-        }
-        params.update(base_manager.default_params)
-        auth_provider = base_manager.auth_provider
+class Clients(clients.ServiceClients):
+    """Tempest stable service clients and loaded plugins service clients"""
 
-        self.consistencygroups_adm_client = (
-            consistencygroups_client.ConsistencyGroupsClient(auth_provider,
-                                                             **params))
-        self.volume_revert_client = (
-            volume_revert_client.VolumeRevertClient(auth_provider, **params))
+    def __init__(self, credentials, service=None):
+        """Emulate the interface of Tempest's clients.Manager"""
+        # Identity settings
+        if CONF.identity.auth_version == 'v2':
+            identity_uri = CONF.identity.uri
+        else:
+            identity_uri = CONF.identity.uri_v3
+        super(Clients, self).__init__(credentials, identity_uri)