Sync policy module from oslo-incubator

Sync policy module from oslo-incubator

The policy module has not had a sync since back in
November.  There have been a number of changes that
should be pulled into Kilo.

Current HEAD in OSLO:
---------------------
commit 9bf01f9d98487cb13e3d95ad2a580fe8fc6f2479
Date:  Fri Feb 13 14:18:58 2015 -0500
Switch from oslo.config to oslo_config

Changes merged with this patch:
---------------------
2aacb111 Change oslo.config to oslo_config
2fbf5065 Remove oslo.log code and clean up versionutils API
262279b1 switch to oslo_serialization
07e9b32a Improving docstrings for policy API
e67f5cd0 Merge "Don't log missing policy.d as a warning"
99d991ce Merge "Fixed a problem with neutron http policy check"
b19af080 Don't log missing policy.d as a warning
2324c775 Add rule overwrite flag to Enforcer class
6166a960 Fixed a problem with neutron http policy check

Closes-bug: 1288178
Change-Id: I6987029b9c15f3d35fa591014859f5f96c98f3a3