move all conf overrides to conf_fixture
move all conf overrides to conf_fixture

Some config overrides were in conf_fixture, and some were living in
test.py:setUp. If we are globally overriding conf variables we should
do it in one place, the fixture.

Change-Id: Ief66e2245179a37eae60bafaf9e8f452d89319a7

citrix-openstack-build/oslo.versionedobjects,openstack/oslo.versionedobjects