Sync periodic_task module from oslo-incubator

Sync periodic_task module from oslo-incubator

We have a need in Cinder to now be able to dynamically
add periodic tasks.  This sync brings in new functionality
that supports that.

Current HEAD in OSLO:
---------------------
commit 03143669d2c996f7c20d2d75f6c67827d2db216a
Date:   Tue Feb 10 11:59:45 2015 -0500
Update policy.py status in MAINTAINERS

Changes merged with this patch:
---------------------
2aacb111 Change oslo.config to oslo_config
2fbf5065 Remove oslo.log code and clean up versionutils API
fbd77a7b Allow overriding name for periodic tasks
9896e0e1 Separate add_periodic_task from the metaclass __init__

Change-Id: If39ce7baddd6ad5325afcd504bab8ac305da939d