Split docker mirror config into its own role

So that the docker mirror configuration can be used without the
install-docker role (e.g., if another process is used to install
docker on a target host), split the part of the role which
configures mirrors into its own role and include it in the
install-docker role.

Change-Id: I7cd7f61e2d1281cd2949c1f69a081c7217d0d328

roles/install-docker/tasks/main.yaml

@@ -1,14 +1,6 @@
-- name: Set mirror_fqdn fact
-  when:
-    - mirror_fqdn is not defined
-    - zuul_site_mirror_fqdn is defined
-  set_fact:
-    mirror_fqdn: "{{ zuul_site_mirror_fqdn }}"
-
 - name: Set up docker mirrors
-  include: mirror.yaml
-  when: mirror_fqdn is defined
-  static: no
+  include_role:
+    name: use-docker-mirror
 
 - name: Install docker-ce from upstream
   include: upstream.yaml

roles/use-docker-mirror/README.rst

@@ -0,0 +1,20 @@
+Configure docker to use mirrors if available.
+
+**Role Variables**
+
+.. zuul:rolevar:: mirror_fqdn
+   :default: {{ zuul_site_mirror_fqdn }}
+
+   The base host for mirror servers.
+
+.. zuul:rolevar:: docker_mirror
+
+   URL to override the generated docker hub mirror url based on
+   :zuul:rolevar:`install-docker.mirror_fqdn`.
+
+.. zuul:rolevar:: docker_insecure_registries
+   :default: undefined
+
+   Declare this with a list of insecure registries to define the
+   registries which are allowed to communicate with HTTP only or
+   HTTPS with no valid certificate.

roles/use-docker-mirror/tasks/main.yaml

@@ -0,0 +1,11 @@
+- name: Set mirror_fqdn fact
+  when:
+    - mirror_fqdn is not defined
+    - zuul_site_mirror_fqdn is defined
+  set_fact:
+    mirror_fqdn: "{{ zuul_site_mirror_fqdn }}"
+
+- name: Set up docker mirrors
+  include: mirror.yaml
+  when: mirror_fqdn is defined
+  static: no

roles/use-docker-mirror/templates/daemon.json.j2

@@ -0,0 +1,4 @@
+{
+  {% if docker_insecure_registries is defined -%}"insecure-registries": {{ docker_insecure_registries | to_json }},{% endif %}
+  "registry-mirrors": ["{{ docker_mirror }}"]
+}