Add support for overlay networks in Swarm.

Built-in in docker >= 1.9, it justs need a K-V store.
This patch reuses the existing etcd supporting Swarm.

Change-Id: Iae2e5aa1d8836d344f16ec911c766c426b1b558a

magnum/drivers/swarm_fedora_atomic_v1/templates/fragments/network-service.sh

@@ -4,6 +4,13 @@
 
 echo "Configuring ${NETWORK_DRIVER} network service ..."
 
+if [ "$NETWORK_DRIVER" == "docker" ]; then
+    DOCKER_NETWORK_OPTIONS="--cluster-store etcd://$ETCD_SERVER_IP:2379\
+ --cluster-advertise $SWARM_NODE_IP:9379"
+    sed -i "/^DOCKER_NETWORK_OPTIONS=/ s#=.*#='$DOCKER_NETWORK_OPTIONS'#" \
+        /etc/sysconfig/docker-network
+fi
+
 if [ "$NETWORK_DRIVER" != "flannel" ]; then
     exit 0
 fi

releasenotes/notes/add-overlay-networks-to-swarm-4467986d7853fcd8.yaml

@@ -0,0 +1,9 @@
+---
+features:
+  - Add configuration for overlay networks for the docker
+    network driver in swarm. To use this feature, users need
+    to create a swarm cluster with network_driver set to 'docker'.
+    After the cluster is created, users can create an overlay network
+    (docker network create -d overlay mynetwork) and use it when
+    launching a new container (docker run --net=mynetwork ...).
+