Fix image publish split

When the image publish job was split [0], only the last variant
of the job (commit hash) was being utilized [1], resulting in the
latest tag no longer being pushed [2]. This fixes this
by creating separate jobs instead of just separate job variants.

[0]: https://review.opendev.org/c/airship/images/+/784703
[1]: https://zuul.openstack.org/builds?job_name=airship-images-publish
[2]: https://quay.io/repository/airshipit/qcow-bundle?tag=latest-ubuntu_focal&tab=tags

Signed-off-by: Sean Eagan <seaneagan1@gmail.com>
Change-Id: Ib5359bafa7699658ee7247b1739929397a489167

.zuul.yaml

@@ -36,10 +36,8 @@
     post:
       jobs:
         - images-upload-git-mirror
-        - airship-images-publish
-        - airship-images-publish:
-            vars:
-              image_tag: "{{ zuul.newrev }}"
+        - airship-images-publish-latest
+        - airship-images-publish-commit
     tag:
       jobs:
         - images-upload-git-mirror
@@ -61,7 +59,7 @@
     post-run: playbooks/airship-collect-logs.yaml
 
 - job:
-    name: airship-images-publish
+    name: airship-images-publish-latest
     nodeset: airship-images-single-node
     timeout: 7200
     post-timeout: 7200
@@ -71,6 +69,12 @@
       - name: airship_images_quay_creds
         secret: airship_images_quay_creds
 
+- job:
+    name: airship-images-publish-commit
+    parent: airship-images-publish-latest
+    vars:
+      image_tag: "{{ zuul.newrev }}"
+
 - job:
     name: images-upload-git-mirror
     parent: upload-git-mirror