Let enforcer.py work under both py2 and py3
Let enforcer.py work under both py2 and py3

I guess the gate uses py3, but some of the post jobs still use py2?
Whatever, it's easy enough to support both.

See http://logs.openstack.org/f9/f9b96861577e26f0540158e00706e2505213f4bf/post/publish-openstack-sphinx-docs/58260e1/ara/result/8a18f0c0-d4b0-4cef-9d31-4cf79f3b4999/
for an example failure.

Change-Id: I37e507d37d4a41f5c55f2314bc074556f6262b50

stackforge/python-openstacksdk,dtroyer/python-openstacksdk,stackforge/python-openstacksdk,openstack/python-openstacksdk,openstack/python-openstacksdk,dtroyer/python-openstacksdk