Sync unified logging solution from Oslo

This commit introduces a unified logging strategy from oslo-incubator in
an attempt to standardize logging in Keystone similar to other OpenStack
projects (Nova, Quantum, etc.). This commit only introduces
oslo-incubator/openstack/common/log.py and it's dependencies.
Implementation of this logging solution will be purposed later.

blueprint unified-logging-in-keystone

Change-Id: I860c0f0e935fcd7b4c4886ffd54bf22f2cf4cbb3