Tell the proxy that multicast is off in awsvpc mode.

Otherwise it will use the regular weavewait program which wait for the
multicast route to be added.

weave

@@ -1689,6 +1689,8 @@ launch_proxy() {
        docker create -v /w -v /w-noop -v /w-nomcast --name=$VOLUMES_CONTAINER_NAME \
            --label=weavevolumes --entrypoint=/bin/false $EXEC_IMAGE >/dev/null
     fi
+    detect_awsvpc
+    [ -n "$AWSVPC" ] && PROXY_ARGS="$PROXY_ARGS --no-multicast-route"
     PROXY_CONTAINER=$(docker run -d --name=$PROXY_CONTAINER_NAME \
         $(docker_run_options) \
         $RESTART_POLICY \