Tenants API Service Tests Parity.

1. Added a service test to identity admin package.
2. Refactored fixtures.
3. Fixed reviewer comment - removed teardown in test_services
4. Flipped up addCleanup to first check the response code.

Change-Id: I431ace431770b5e28067db59bf644217bc3cbb1c
Merge "Tenants API Service Tests Parity."