Compatibility fixes for Python 3.3

1) Added a py33 environment to tox
2) Updated tests to mock the correctly named builtins.open based on
python version
3) Other minor compatibility fixes

Tests for Python 3.3 will not pass due to this bug:
https://github.com/eventlet/eventlet/issues/83 among possibly others in
eventlet.

Change-Id: Ie4b512a926fa690ee77a71a89851c871ea1f6be0

ironic_python_agent/utils.py

@@ -15,7 +15,6 @@ limitations under the License.
 """
 
 import collections
-import ordereddict
 
 from ironic_python_agent.openstack.common import gettextutils as gtu
 from ironic_python_agent.openstack.common import log as logging
@@ -29,6 +28,7 @@ def get_ordereddict(*args, **kwargs):
     try:
         return collections.OrderedDict(*args, **kwargs)
     except AttributeError:
+        import ordereddict
         return ordereddict.OrderedDict(*args, **kwargs)