promote-docker-image: improve failure debugability

Currently this no_logs the entire selection and delete loop, which is
probably maximal efficiency but makes it very hard to debug on failure
(which we are seeing).  This extracts the list creation and uri call
so we can see the tags it is trying to delete.

Change-Id: I93fd19aedaa9fc328a1a347986a5f0c20439d476

roles/promote-docker-image/tasks/delete-tag.yaml

@@ -0,0 +1,12 @@
+- name: Show the tag we are about to delete
+  debug:
+    var: zj_docker_tag
+
+- name: Make delete call
+  no_log: true
+  uri:
+    url: "https://hub.docker.com/v2/repositories/{{ zj_image.repository }}/tags/{{ zj_docker_tag.name }}/"
+    method: DELETE
+    status_code: [200, 204]
+    headers:
+      Authorization: "JWT {{ jwt_token.json.token }}"

roles/promote-docker-image/tasks/promote-cleanup.yaml

@@ -3,18 +3,24 @@
     url: "https://hub.docker.com/v2/repositories/{{ zj_image.repository }}/tags?page_size=1000"
     status_code: 200
   register: tags
-- name: Delete all change tags older than the cutoff
-  no_log: true
+
+- name: Create old tags list
+  set_fact:
+    _old_tags: []
+
+- name: Build list of old tags
   loop: "{{ tags.json.results }}"
   loop_control:
     loop_var: zj_docker_tag
+  set_fact:
+    _old_tags: '{{ _old_tags.append(zj_docker_tag) }}'
   when:
     - zj_docker_tag.name.startswith('change_') or zj_docker_tag.name.startswith(zuul.pipeline)
     # Was updated > 24 hours ago:
     - "((ansible_date_time.iso8601 | regex_replace('^(....-..-..)T(..:..:..).*Z', '\\\\1 \\\\2') | to_datetime) - (zj_docker_tag.last_updated | regex_replace('^(....-..-..)T(..:..:..).*Z', '\\\\1 \\\\2') | to_datetime)).seconds > 86400"
-  uri:
-    url: "https://hub.docker.com/v2/repositories/{{ zj_image.repository }}/tags/{{ zj_docker_tag.name }}/"
-    method: DELETE
-    status_code: [200, 204]
-    headers:
-      Authorization: "JWT {{ jwt_token.json.token }}"
+
+- name: Delete all change tags older than the cutoff
+  loop: "{{ _old_tags }}"
+  loop_control:
+    loop_var: zj_docker_tag
+  include_tasks: delete-tag.yaml