Replace dict.iteritems() with six.iteritems()

dict.iteritems() was replaced with dict.items() in Python 3. Use the
six.iteritems() function to get code compatible with Python 2 and Python 3.

Change-Id: I0c8ecc3ae540ffaf4c6b159e09ca16ccf365973d

tests/utils.py

@@ -25,6 +25,7 @@ import os
 
 import fixtures
 from oslo.config import cfg
+import six
 import testtools
 
 from oslo.messaging.openstack.common.fixture import moxstubout
@@ -79,5 +80,5 @@ class BaseTestCase(testtools.TestCase):
         test by the tearDown() method.
         """
         group = kw.pop('group', None)
-        for k, v in kw.iteritems():
+        for k, v in six.iteritems(kw):
             self.conf.set_override(k, v, group)