Fix cleanup cmd for assigning role to user

assign_user_role method was moved to roles_client
so should use that service client instead of identity client.

Change-Id: I6c06a47f3e15eb842e3965fc7a5df676cddaeedb
Closes-Bug: #1546379
diff --git a/tempest/cmd/cleanup.py b/tempest/cmd/cleanup.py
index 7b73a61..c8a8159 100644
--- a/tempest/cmd/cleanup.py
+++ b/tempest/cmd/cleanup.py
@@ -231,7 +231,6 @@
         return 'Cleanup after tempest run'
 
     def _add_admin(self, tenant_id):
-        id_cl = self.admin_mgr.identity_client
         rl_cl = self.admin_mgr.roles_client
         needs_role = True
         roles = rl_cl.list_user_roles(tenant_id, self.admin_id)['roles']
@@ -241,7 +240,7 @@
                 LOG.debug("User already had admin privilege for this tenant")
         if needs_role:
             LOG.debug("Adding admin privilege for : %s" % tenant_id)
-            id_cl.assign_user_role(tenant_id, self.admin_id,
+            rl_cl.assign_user_role(tenant_id, self.admin_id,
                                    self.admin_role_id)
             self.admin_role_added.append(tenant_id)