Periodic jobs don't have zuul.change defined, since there is no change
being tested. This causes an early failure when referencing zuul.change
to set the image tag for built images. In periodic jobs we'll never need
to build images because there is no dependent kolla change under test.
Change-Id: I6d9d81cf17b7d0d7aaf87cd96418c904c46681f2
2b7a9dc207