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
Merge "Update service test case - V3"