Dogfood infra jobs on Ubuntu/Quantal slaves.

As part of a phased approach to starting testing on Ubuntu/Quantal,
we're first moving openstack-infra jobs to them before risking more
project-wide disruption.

Change-Id: I65d8ea3b798ac06f138a364c9656476dab35eaca
Reviewed-on: https://review.openstack.org/23841
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins