Update service test case - V3

Adds a test_services.py test script so as to validate the update
service. And the rescpective support methods to "service_client.py"
in both json and xml interfaces

Change-Id: Ic088861049a2642076bbca166c84f234dfb6a290
Implements: blueprint keystone-v3-service-api-test
diff --git a/tempest/tests/identity/base.py b/tempest/tests/identity/base.py
index 718b74f..6980425 100644
--- a/tempest/tests/identity/base.py
+++ b/tempest/tests/identity/base.py
@@ -30,6 +30,7 @@
         cls.token_client = os.token_client
         cls.endpoints_client = os.endpoints_client
         cls.v3_client = os.identity_v3_client
+        cls.service_client = os.service_client
 
         if not cls.client.has_admin_extensions():
             raise cls.skipException("Admin extensions disabled")