Use ReplaceEngineFacade fixture
Use ReplaceEngineFacade fixture

Now that the previous patch Ifc070d19a18a2d66f1a7bd5898428b12901dfe9e moved
most of the logic to the setUp of the Database fixture we can replace
our direct factory patching with the ReplaceEngineFacade fixture from
oslo_db.

Change-Id: Icd25adcc931cae2126e03c00af7e4420d3781b9a

mahak/nova,mahak/nova,openstack/nova,openstack/nova,mahak/nova,openstack/nova