Drop OfficialClientManager from tenant isolation

Scenario tests use the tempest clients, so drop support for
OfficialClientManager from the tenant isolation classes.

Change-Id: I84638210043d376b4f4025a69751536651991293
Partially-implements: bp:tempest-client-scenarios
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index 9933646..559f3d5 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -62,8 +62,7 @@
         super(ScenarioTest, cls).setUpClass()
         # Using tempest client for isolated credentials as well
         cls.isolated_creds = isolated_creds.IsolatedCreds(
-            cls.__name__, tempest_client=True,
-            network_resources=cls.network_resources)
+            cls.__name__, network_resources=cls.network_resources)
         cls.manager = clients.Manager(
             credentials=cls.credentials()
         )