Add optional internal gearman server.

Change-Id: Id4e6b77f5abba23f46236def28f54509c61fd247
Reviewed-on: https://review.openstack.org/30170
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins