Add a test for changes that trigger multiple pipelines.

Change-Id: I147491d2c08fa1040f41f0c299113e3eb8968252
Reviewed-on: https://review.openstack.org/29158
Reviewed-by: Antoine Musso <hashar@free.fr>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins