Add role for adding docker nodes to swarm

roles/swarm/templates/daemon.json.j2

@@ -0,0 +1,7 @@
+{
+    "dns": [
+        {% for dns_server in _docker_daemon_dns %}
+        "{{ dns_server }}"{{ ',' if not loop.last else '' }}
+        {% endfor %}
+    ]
+}