There is no this directory openstack/common which was used
to keep codes from oslo-incubator, we have retired oslo-incubator.
Removing openstack/commonfrom all OpenStack code in favor of the
Oslo libraries is a project wide goal for the Ocata release. So
don't use this directory any more. We should drop it for improving
searching efficiency.
Change-Id: Id4ff616ccb2dd28dac6d6ac40c9637644b783343