Use testtools as the base testcase class.
Use testtools as the base testcase class.

As a step towards parallelizing the test runs, use testtools as the
base unittest test case class. In this patch, it has caused us to catch
places where setUp and tearDown were not being chained properly.
Additionally, we get to remove our custom skip decorators and a few
backported assert calls.

Part of blueprint grizzly-testtools

Change-Id: Ia2025e1b7191b65130b85b30ce6239d5c431c8ba

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