Import StringIO from six in a couple more places.

v2/ansible/executor/module_common.py

@@ -21,7 +21,7 @@ from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
 # from python and deps
-from cStringIO import StringIO
+from six.moves import StringIO
 import json
 import os
 import shlex

v2/test/parsing/yaml/test_loader.py

@@ -20,7 +20,7 @@
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
-from StringIO import StringIO
+from six.moves import StringIO
 from collections import Sequence, Set, Mapping
 
 from ansible.compat.tests import unittest