Start adding reusable test fixtures.
Start adding reusable test fixtures.

Now that nova is using fixtures, we have grown some that can be used across
projects. The mox/stubout fixture is a great example of this - and also can
be used in the oslo tests themselves.

Change-Id: Ia78019317a6772c5c66a875c948854248383f9ea

openstack/oslo.concurrency,JioCloud/oslo.concurrency,varunarya10/oslo.concurrency