Handle Docker rpm updates

The tasks were taken from OpenStack TripleO. They manage the case where
Docker needs to be updated. We'll first stop containers, stop docker
then update the rpm before making sure Docker is running again.

Change-Id: Ibde3d326b7e824fe09fafb9f46875b1e6739d299

tasks/docker-update.yml

@@ -0,0 +1,28 @@
+# tasks file for ansible-role-container-registry
+# the tasks will ensure docker is up to date.
+
+- name: can docker be updated
+  shell: yum check-update docker
+  register: docker_check_update
+  failed_when: docker_check_update.rc not in [0, 100]
+  changed_when: docker_check_update.rc == 100
+
+- name: set docker_rpm_needs_update fact
+  set_fact: docker_rpm_needs_update={{ docker_check_update.rc == 100 }}
+
+- name: stop all containers before update
+  # xargs is preferable to docker stop $(docker ps -q) as that might generate a
+  # a too long command line
+  shell: docker ps -q | xargs --no-run-if-empty -n1 docker stop
+  when: docker_rpm_needs_update
+
+- name: ensure docker is installed
+  yum:
+    name: docker
+    state: present
+  when: docker_rpm_needs_update
+
+- name: update the docker package
+  yum: name=docker state=latest update_cache=yes # cache for https://bugs.launchpad.net/tripleo/+bug/1703830
+  when: docker_rpm_needs_update
+  notify: restart docker service