weave launch-router wasn't returning the correct container id

since $CONTAINER gets stomped on by various functions, in particular
populate_dns.

Broken by #1065.

weave

@@ -1092,14 +1092,14 @@ launch_router() {
     # Set WEAVE_DOCKER_ARGS in the environment in order to supply
     # additional parameters, such as resource limits, to docker
     # when launching the weave container.
-    CONTAINER=$(docker run --privileged -d --name=$CONTAINER_NAME \
+    ROUTER_CONTAINER=$(docker run --privileged -d --name=$CONTAINER_NAME \
         -p $PORT:$CONTAINER_PORT/tcp -p $PORT:$CONTAINER_PORT/udp \
         -p $DOCKER_BRIDGE_IP:53:53/udp -p $DOCKER_BRIDGE_IP:53:53/tcp \
         -v /var/run/docker.sock:/var/run/docker.sock \
         -e WEAVE_PASSWORD \
         -e WEAVE_CIDR=none \
         $WEAVE_DOCKER_ARGS $IMAGE $COVERAGE_ARGS --iface $CONTAINER_IFNAME --port $CONTAINER_PORT --name "$PEERNAME" --nickname "$(hostname)" --ipalloc-range "$IPRANGE" "$@")
-    with_container_netns_or_die $CONTAINER launch
+    with_container_netns_or_die $ROUTER_CONTAINER launch
     wait_for_status $CONTAINER_NAME $HTTP_PORT
     if [ -n "$IPRANGE" ] ; then
         # Tell the newly-started weave IP allocator about existing weave IPs
@@ -1250,7 +1250,7 @@ case "$COMMAND" in
         deprecation_warnings "$@"
         check_not_running $CONTAINER_NAME $BASE_IMAGE
         launch_router "$@"
-        echo $CONTAINER
+        echo $ROUTER_CONTAINER
         ;;
     launch-proxy)
         deprecation_warnings "$@"