Add packagekit module.

This module supports automatic upgrades on RHEL/Centos slaves.
It works by installing PackageKit-cron and updating the config
file to enable automatic updates.

PackageKit-cron runs once a day via cron.

Fixes LP Bug #1180948.

Change-Id: I901ebf5f48fabee9456333ade0c141beacac62e6
Reviewed-on: https://review.openstack.org/29422
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins