Disable broken image building

The periodic jobs for building images are all failing, add some
low-hanging fruits for fixing:

1) Remove usage of own Fedora image build tools, they were removed as
   part of change Ie6a8496c202ff0bf330dd0f434cff8777e5ef112.
2) Add openstack/tripleo-image-elements and
   openstack/heat-templates as required-repo for the build
   jobs, they are requirements.

Still, these are still failing, let's disable the periodic jobs.
They have been broken since ages without fixing. There's no
record of a successful run under Zuul v3.
Last images at http://tarballs.openstack.org/magnum/images/ are from
2017.

Change-Id: I01122fa029b4124d912e80ea43bca07b8f2ebe5c

.zuul.yaml

@@ -321,6 +321,8 @@
       - openstack/dib-utils
       - openstack/diskimage-builder
       - openstack/magnum
+      - openstack/heat-templates
+      - openstack/tripleo-image-elements
 
 - job:
     name: magnum-dib-buildimage-fedora-atomic-25
@@ -396,11 +398,13 @@
         - magnum-functional-swarm-ironic
         - magnum-functional-k8s-multinode
         - magnum-functional-swarm-mode-multinode
-    periodic:
-      jobs:
-        - magnum-dib-buildimage-fedora-atomic-25
-        - magnum-dib-buildimage-ubuntu-mesos
-        - magnum-dib-buildimage-centos-dcos
+    # XXX: The periodic jobs are completely broken and need to be fixed,
+    # enable them once they work again.
+    # periodic:
+    #   jobs:
+    #     - magnum-dib-buildimage-fedora-atomic-25
+    #     - magnum-dib-buildimage-ubuntu-mesos
+    #     - magnum-dib-buildimage-centos-dcos
     post:
       jobs:
         - magnum-container-publish

playbooks/magnum-buildimages-base.yaml

@@ -77,9 +77,7 @@
 
               #TODO: Add size validation
           else
-              MAGNUM_ELEMENTS=./openstack/magnum/magnum/drivers/common/image
-              export ELEMENTS_PATH=$DIB_ELEMENTS:$MAGNUM_ELEMENTS
-              $MAGNUM_ELEMENTS/fedora-atomic/install_imagebuild_deps.sh
+              export ELEMENTS_PATH=$DIB_ELEMENTS
 
               export DIB_RELEASE="25"
 
@@ -90,8 +88,6 @@
 
               disk-image-create -x -o $WORKSPACE/{{ image_name }}-dib fedora-atomic
 
-              # validate image
-              $MAGNUM_ELEMENTS/fedora-atomic/validate_atomic_image.sh $WORKSPACE/{{ image_name }}-dib.qcow2
           fi
 
           set +u