Add hacking check for testtools.skip

Adding hacking check for testtools.skip decorator as described
in the bug referenced below.

Closes-Bug: #1490590
Change-Id: I9c456bb8b57a54fbcd1cd5249eec2292916d4ff9
diff --git a/tempest/tests/test_hacking.py b/tempest/tests/test_hacking.py
index 9bc9cfe..62d2aee 100644
--- a/tempest/tests/test_hacking.py
+++ b/tempest/tests/test_hacking.py
@@ -138,3 +138,11 @@
 
         self.assertEqual(0, len(list(checks.no_mutable_default_args(
             "defined, undefined = [], {}"))))
+
+    def test_no_testtools_skip_decorator(self):
+        self.assertEqual(1, len(list(checks.no_testtools_skip_decorator(
+            " @testtools.skip('Bug xxx')"))))
+        self.assertEqual(0, len(list(checks.no_testtools_skip_decorator(
+            " @testtools.skipUnless(CONF.something, 'msg')"))))
+        self.assertEqual(0, len(list(checks.no_testtools_skip_decorator(
+            " @testtools.skipIf(CONF.something, 'msg')"))))