Move docker systemd unit creation to docker role

Creating the unit using default settings early on
and then changing it during network_plugin section
leads to too many docker restarts and duplicated code.

Reversed Wants= dependence on docker.service so it does not
restart docker when reloading systemd

Consolidated all docker restart handlers.

roles/docker/tasks/main.yml

@@ -59,6 +59,14 @@
   when: ansible_service_mgr == "systemd" and
         (http_proxy is defined or https_proxy is defined or no_proxy is defined)
 
+- name: Write docker.service systemd file
+  template:
+    src: systemd-docker.service.j2
+    dest: /etc/systemd/system/docker.service
+  register: docker_service_file
+  notify: restart docker
+  when: ansible_service_mgr == "systemd" and ansible_os_family != "CoreOS"
+
 - meta: flush_handlers
 
 - name: ensure docker service is started and enabled