Allow replacing tuns.sh tunnels with an optional? flag

Currently it can happen that a tunnel is broken due to a network error but does not time out fast enough. In such cases the node might try to reestablish the tunnel and get redirected to a random other one.

It would be nice to be able to specify a flag that kills the old/other connection and takes over the tunnel.

This might also be somewhat related to the load-balancing feature.