Always trigger docker restart when docker package changes

Docker upgrade doesn't auto-restart docker, causing failures
when trying to start another container

roles/docker/tasks/main.yml

@@ -65,6 +65,7 @@
   retries: 4
   delay: "{{ retry_stagger | random + 3 }}"
   with_items: "{{ docker_package_info.pkgs }}"
+  notify: restart docker
   when: (not ansible_os_family in ["CoreOS", "Container Linux by CoreOS"]) and (docker_package_info.pkgs|length > 0)
 
 - name: check minimum docker version for docker_dns mode. You need at least docker version >= 1.12 for resolvconf_mode=docker_dns