Deprecate MoxStubout class

As part of the mox removal goal, we need to deprecate this class so
it can be removed once everyone has stopped using it.

Story 2001546

Change-Id: I8864ab0c475b63a7549137d9ea0514b7e8154e79

oslotest/moxstubout.py

@@ -15,10 +15,12 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+from debtcollector import removals
 import fixtures
 from mox3 import mox
 
 
+@removals.removed_class('MoxStubout', version='3.5.0')
 class MoxStubout(fixtures.Fixture):
     """Deal with code around mox and stubout as a fixture."""
 

requirements.txt

@@ -10,3 +10,4 @@ testtools>=2.2.0 # MIT
 mock>=2.0.0 # BSD
 mox3>=0.20.0 # Apache-2.0
 os-client-config>=1.28.0 # Apache-2.0
+debtcollector  # Apache-2.0