Apply requested tags locally for docker build

When doing the local build, go ahead and apply the tags to the
local image, so that one can use the role for building local
images for testing that will eventually be published with the given
tag.

Change-Id: I0249ddc4f9a8a2e17466f96a5711672282ce025c

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

@@ -8,6 +8,9 @@
       --build-arg {{ build_arg }}
     {% endfor -%}
     --tag {{ item.repository }}:change_{{ zuul.change }}
+    {% for tag in item.tags | default(['latest']) -%}
+    --tag {{ item.repository }}:{{ tag }}
+    {% endfor -%}
   args:
     chdir: "{{ zuul_work_dir }}/{{ item.context }}"
   loop: "{{ docker_images }}"