Httpretty will work in exactly the same way regardless of whether we use
the httplib or requests library. Convert it so we can modify the
middleware and know that our tests are still correct.
In this process we also split the tests from having V3 tests override
V2 tests, to having a base test class and V2 and V3 seperate overrides.
Change-Id: I1bfcecc6ae47a6dd5e76d4ceb8b3941e6ad1089f