Fix the usage of tempest.client.Manager class

This should fix our gate. We should continue the work to remove
the dependencies from any module that isn't at tempest.lib.

Change-Id: I2158d1971a4187171a89169c3f324453f0ec13be
diff --git a/keystone_tempest_plugin/clients.py b/keystone_tempest_plugin/clients.py
index 9865b91..97b5b14 100644
--- a/keystone_tempest_plugin/clients.py
+++ b/keystone_tempest_plugin/clients.py
@@ -26,8 +26,8 @@
 
 class Manager(clients.Manager):
 
-    def __init__(self, credentials, service=None):
-        super(Manager, self).__init__(credentials, service)
+    def __init__(self, credentials):
+        super(Manager, self).__init__(credentials)
 
         self.auth_client = auth_client.AuthClient(self.auth_provider)
         self.identity_providers_client = (