Client tests are broadly seperated into v2 and v3. These folders don't
distinguish between the tests that are on v2/v3 auth and those that are
CRUD related. This means that the base v2 and v3 test class always
create a client object for the tests to use, even if they don't need it.
Whilst this isn't a big deal now, we want to be able to seperate only
those tests that require a client so we can test them with multiple
different styles of client.
Add a new ClientTestCase class that will construct a client object for
the tests that need it.
Change-Id: I61f463ac5e878107c1889672f4d4cf5874821363
2dd67f8a00