Make Marathon and Chronos tests more deterministic

The --force value is overriden on tests which check force mode.
Unfortunately, when the test written for non-force mode is
running after the force mode, the old config override is still
remaining. This commit ensures that for non-force mode, the
--force flag is disabled.

Change-Id: I045c9e7ea05a54f82ea4a1f58b03625e84df0489
Closes-Bug: 1526340

kolla_mesos/tests/test_chronos.py

@@ -73,6 +73,7 @@ class TestClient(base.BaseTestCase):
     @mock.patch.object(chronos, 'LOG')
     @requests_mock.mock()
     def test_add_job_already_existing(self, log_mock, req_mock):
+        CONF.set_override('force', False)
         req_mock.get('http://localhost:4400/scheduler/jobs', json=[{
             'name': '/keystone-bootstrap'
         }])

kolla_mesos/tests/test_marathon.py

@@ -53,6 +53,7 @@ class TestMarathonClient(base.BaseTestCase):
 
     @mock.patch.object(marathon, 'LOG')
     def test_add_app_already_existing(self, log_mock):
+        CONF.set_override('force', False)
         with mock.patch.object(
             self.client, 'get_app', return_value={'id': 'my-app',
                                                   'other_param': 'the-old-one'}