Cleanup time patching

Rather than create a mock and have to stop it, use
fixtures.MockPatchObject since it encapsulates the cleanup.

Change-Id: I431c480c9bb8bed07a108f088ac9d91872777754

keystoneauth1/tests/unit/utils.py

@@ -16,7 +16,6 @@ import time
 import uuid
 
 import fixtures
-import mock
 import requests
 from requests_mock.contrib import fixture
 import six
@@ -42,15 +41,11 @@ class TestCase(testtools.TestCase):
     def setUp(self):
         super(TestCase, self).setUp()
         self.logger = self.useFixture(fixtures.FakeLogger(level=logging.DEBUG))
-        self.time_patcher = mock.patch.object(time, 'time', lambda: 1234)
-        self.time_patcher.start()
+
+        fixtures.MockPatchObject(time, 'time', lambda: 1234)
 
         self.requests_mock = self.useFixture(fixture.Fixture())
 
-    def tearDown(self):
-        self.time_patcher.stop()
-        super(TestCase, self).tearDown()
-
     def stub_url(self, method, parts=None, base_url=None, json=None, **kwargs):
         if not base_url:
             base_url = self.TEST_URL