Replace auth_token middleware tests with httpretty
Replace auth_token middleware tests with httpretty

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

jamielennox/python-keystoneclient,metacloud/python-keystoneclient,jamielennox/python-keystoneclient,ntt-sic/python-keystoneclient,citrix-openstack-build/python-keystoneclient,darren-wang/ksc,ntt-sic/python-keystoneclient,sdpp/python-keystoneclient,metacloud/python-keystoneclient,citrix-openstack-build/python-keystoneclient,Mercador/python-keystoneclient,alexpilotti/python-keystoneclient,klmitch/python-keystoneclient,ging/python-keystoneclient,klmitch/python-keystoneclient,citrix-openstack-build/python-keystoneclient,jamielennox/python-keystoneclient,Mercador/python-keystoneclient,ntt-sic/python-keystoneclient,sdpp/python-keystoneclient,magic0704/python-keystoneclient,darren-wang/ksc,magic0704/python-keystoneclient,ging/python-keystoneclient,alexpilotti/python-keystoneclient