Sync oslo's policy module

I made some changes to the policy module in oslo to use six.moves.urllib
instead of py3kcompat.urlutils. This change will help us on our way to
being more Python3 friendly.

Our test_policy tests had to be updated because we are stubbing
implementation details in policy.

Change-Id: I23377a4c71f0f0cb58518f0cd5ce341a8a9c4243
Implements: bp keystone-py3kcompat
Merge "Sync oslo's policy module"