Use six.StringIO/BytesIO instead of StringIO.StringIO

to keep Python 3.x compatibility, use six.StringIO/BytesIO to
replace StringIO.StringIO

StringIO works for unicode
BytesIO works for bytes

Change-Id: I0d1f8a55c3bc41379077b46feb81931779b7ad45
Partial-Bug: #1280100

ironic/tests/test_utils.py

@@ -20,13 +20,13 @@ import errno
 import hashlib
 import os
 import os.path
-import StringIO
 import tempfile
 import uuid
 
 import mock
 import netaddr
 from oslo.config import cfg
+import six
 
 from ironic.common import exception
 from ironic.common import utils
@@ -233,7 +233,7 @@ class GenericUtilsTestCase(base.TestCase):
 
     def test_hash_file(self):
         data = 'Mary had a little lamb, its fleece as white as snow'
-        flo = StringIO.StringIO(data)
+        flo = six.StringIO(data)
         h1 = utils.hash_file(flo)
         h2 = hashlib.sha1(data).hexdigest()
         self.assertEqual(h1, h2)