Fix pin images task with atmosphere_image_prefix

This change also includes a skip for running jobs when any changes
in the `build` folder are done.

Change-Id: I632a2d71beb4227f9067ed936550a714df269232
(cherry picked from commit f6e53de13321bbc425813a5fcb934fb954d8ec66)
diff --git a/zuul.d/jobs.yaml b/zuul.d/jobs.yaml
index 4390d06..99662e4 100644
--- a/zuul.d/jobs.yaml
+++ b/zuul.d/jobs.yaml
@@ -73,6 +73,7 @@
     run: zuul.d/playbooks/molecule/run.yml
     post-run: zuul.d/playbooks/molecule/post.yml
     irrelevant-files:
+      - ^build/
       - ^doc/
       - ^releasenotes/