Fix format issue

In a previously merged commit, I had confused jjb templating
interpolation to bash variable interpolation (and conflated the two).

this commit resolves the issue so that the jobs are built as expected.

Change-Id: Ie223be4c7990b4c758b06daba8fffcd24110b7fa
Reviewed-on: https://review.openstack.org/26444
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Dan Prince <dprince@redhat.com>
Approved: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins