Don't run swift bitrot jobs.

openstack-stable-maint has no involvement with swift stable branches.
Neither does anyone else.

Change-Id: Ic5a20daeccabad182c396dbdcf34d9b1d969f01b
Reviewed-on: https://review.openstack.org/18901
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins