Replace Mox with Mock

According to [1] "New test cases should be implemented using Mock.
It is part of the Python standard library in Python 3 and as such
is the preferred method for OpenStack." So let's kill Mox in favor
of Mock.

[1] http://docs.openstack.org/infra/manual/developers.html#peer-review

Change-Id: I0db1cf3969a8d5ae90e1a13330799e69c7751207
diff --git a/tempest/tests/test_microversions.py b/tempest/tests/test_microversions.py
index 1ac1232..b80cf80 100644
--- a/tempest/tests/test_microversions.py
+++ b/tempest/tests/test_microversions.py
@@ -57,8 +57,8 @@
     def setUp(self):
         super(TestMicroversionsTestsClass, self).setUp()
         self.useFixture(fake_config.ConfigFixture())
-        self.stubs.Set(config, 'TempestConfigPrivate',
-                       fake_config.FakePrivate)
+        self.patchobject(config, 'TempestConfigPrivate',
+                         fake_config.FakePrivate)
 
     def _test_version(self, cfg_min, cfg_max,
                       expected_pass_tests,