Remove Keystone specific logging module

A unified logging implementation from Oslo-incubator has been carried
over and implemented in Keystone. This is removing the old
keystone/common/logging.py module as it is no longer needed.
Logging in Keystone is now implemented through
keystone/openstack/common/log.py and maintained through Oslo-incubator,
consistent with other logging implementations in OpenStack projects.

blueprint unified-logging-in-keystone

Change-Id: Ib9328a80f60b0b6ec7430d05077aa1a0419e05ac
Merge "Remove Keystone specific logging module"