Use config fixture to avoid racing on self.flags()

Previously self.flags() set options on the global CONF singleton. This
created races where a test running in parallel would end up with
a flag value intended for another test. By using the fixture we scope
self.flags() to each individual test.

Change-Id: Id317e4b86cf7e66172040c23dc3ccf96e820204a

whitebox_tempest_plugin/tests/base.py

@@ -12,6 +12,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+from oslo_config import fixture as config_fixture
 from oslotest import base
 from tempest import config
 
@@ -20,6 +21,10 @@ CONF = config.CONF
 
 class WhiteboxPluginTestCase(base.BaseTestCase):
 
+    def setUp(self):
+        super(WhiteboxPluginTestCase, self).setUp()
+        self.useFixture(config_fixture.Config(CONF))
+
     def flags(self, **kw):
         """Override flag variables for a test."""
         group = kw.pop('group', None)