Use WEAVE_PASSWORD environment variable, if no args supplied

weave

@@ -483,7 +483,7 @@ case "$COMMAND" in
         # when launching the weave container.
         CONTAINER=$(docker run --privileged -d --name=$CONTAINER_NAME \
             -p $PORT:$PORT/tcp -p $PORT:$PORT/udp \
-            $PASSWORD_ARGS \
+            ${PASSWORD_ARGS:-"-e WEAVE_PASSWORD"} \
             $WEAVE_DOCKER_ARGS $IMAGE -name $MACADDR -iface $CONTAINER_IFNAME "$@")
         with_container_netns $CONTAINER launch >/dev/null
         echo $CONTAINER