This commit adds the first missing unit tests to the token clients.
Previously there was no coverage at all for these clients so
there was no in-tree method for verifying the functionality of these
classes. The coverage of this commit is limited and only covers 2
basic uses of the auth() method in both the v2 and v3 token clients.
It will be expanded in future patches. As part of enabling this
coverage the fake_http class had to be modified to return a user
provided body and response code.
Change-Id: I1888b31550e5db4343003b05c0f6865444756789
1efd3a4664