Use testtools as test base class.

On the path to testr migration, we need to replace the unittest base classes
with testtools.
Replace tearDown with addCleanup, addCleanup is more resilient than tearDown.
The fixtures library has excellent support for managing and cleaning
tempfiles. Use it.
Replace skip_ with testtools.skipTest

Part of blueprint grizzly-testtools.

Change-Id: I45e11bbb1ff9b31f3278d3b016737dcb7850cd98

tests/unit/test_jsonutils.py

@@ -17,13 +17,13 @@
 
 import datetime
 import StringIO
-import unittest
+import testtools
 import xmlrpclib
 
 from openstack.common import jsonutils
 
 
-class JSONUtilsTestCase(unittest.TestCase):
+class JSONUtilsTestCase(testtools.TestCase):
 
     def test_dumps(self):
         self.assertEqual(jsonutils.dumps({'a': 'b'}), '{"a": "b"}')
@@ -36,7 +36,7 @@ class JSONUtilsTestCase(unittest.TestCase):
         self.assertEqual(jsonutils.load(x), {'a': 'b'})
 
 
-class ToPrimitiveTestCase(unittest.TestCase):
+class ToPrimitiveTestCase(testtools.TestCase):
     def test_list(self):
         self.assertEquals(jsonutils.to_primitive([1, 2, 3]), [1, 2, 3])