Don't repeat the etc/alias setup for buildset registry pushes

This is currently run for each image that is built; we only need
to run it once.

Change-Id: I45cdf6caaaa0e3a5ebc6bc7f0fcb96f3ea47b9a8

roles/build-docker-image/tasks/main.yaml

@@ -20,6 +20,26 @@
   args:
     chdir: "{{ zuul_work_dir }}/{{ item.context }}"
   loop: "{{ docker_images }}"
+# Docker doesn't understand docker push [1234:5678::]:5000/image/path:tag
+# so we set up /etc/hosts with a registry alias name to support ipv6 and 4.
+- name: Configure /etc/hosts for buildset_registry to workaround docker not understanding ipv6 addresses
+  become: yes
+  lineinfile:
+    path: /etc/hosts
+    state: present
+    regex: "^{{ buildset_registry.host }}\tzuul-jobs.buildset-registry$"
+    line: "{{ buildset_registry.host }}\tzuul-jobs.buildset-registry"
+    insertafter: EOF
+  when: buildset_registry.host | ipaddr
+- name: Set buildset_registry alias variable when using ip
+  set_fact:
+    buildset_registry_alias: zuul-jobs.buildset-registry
+  when: buildset_registry.host | ipaddr
+- name: Set buildset_registry alias variable when using name
+  set_fact:
+    buildset_registry_alias: "{{ buildset_registry.host }}"
+  when: not ( buildset_registry.host | ipaddr )
+# Push each image.
 - name: Push image to buildset registry
   when: buildset_registry is defined
   include_tasks: push.yaml

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

@@ -1,23 +1,3 @@
-# Docker doesn't understand docker push [1234:5678::]:5000/image/path:tag
-# so we set up /etc/hosts with a registry alias name to support ipv6 and 4.
-- name: Configure /etc/hosts for buildset_registry to workaround docker not understanding ipv6 addresses
-  become: yes
-  lineinfile:
-    path: /etc/hosts
-    state: present
-    regex: "^{{ buildset_registry.host }}\tzuul-jobs.buildset-registry$"
-    line: "{{ buildset_registry.host }}\tzuul-jobs.buildset-registry"
-    insertafter: EOF
-  when: buildset_registry.host | ipaddr
-- name: Set buildset_registry alias variable when using ip
-  set_fact:
-    buildset_registry_alias: zuul-jobs.buildset-registry
-  when: buildset_registry.host | ipaddr
-- name: Set buildset_registry alias variable when using name
-  set_fact:
-    buildset_registry_alias: "{{ buildset_registry.host }}"
-  when: not ( buildset_registry.host | ipaddr )
-
 - name: Tag image for buildset registry
   command: >-
     docker tag {{ image.repository }}:{{ image_tag }} {{ buildset_registry_alias }}:{{ buildset_registry.port }}/{{ image.repository }}:{{ image_tag }}