Allow upload-docker-image role to be used outside of promote

This adds an option to the upload-docker-image role so that a job
can be written to run build-docker-image and upload-docker-image
in a release pipeline.  This lets users build tagged docker images
from release tags rather than using the promote pipeline (which
may have built the image before a release git tag was applied).

Change-Id: Id28d0a85e02e56640911c44ddbfff7b38547b0b4

roles/upload-docker-image/README.rst

@@ -1,3 +1,13 @@
 Upload one or more docker images.
 
 .. include:: ../../roles/build-docker-image/common.rst
+
+.. zuul:rolevar:: upload_docker_image_promote
+   :type: bool
+   :default: true
+
+   If ``true`` (the default), then this role will upload the image(s)
+   to Docker Hub with special tags designed for use by the
+   :zuul:role:`promote-docker-image` role.  Set to ``false`` to use
+   this role to directly upload images with the final tag (e.g., as
+   part of an un-gated release job).

roles/upload-docker-image/defaults/main.yaml

@@ -1,2 +1,3 @@
 zuul_work_dir: "{{ zuul.project.src_dir }}"
 docker_dockerfile: "Dockerfile"
+upload_docker_image_promote: true

roles/upload-docker-image/tasks/push.yaml

@@ -1,5 +1,5 @@
 - name: Upload tag to dockerhub
-  command: "docker push {{ zj_image.repository }}:change_{{ zuul.change }}_{{ zj_image_tag }}"
+  command: "docker push {{ zj_image.repository }}:{{ upload_docker_image_promote | ternary('change_' + zuul.change + '_', '') }}{{ zj_image_tag }}"
   loop: "{{ zj_image.tags | default(['latest']) }}"
   loop_control:
     loop_var: zj_image_tag