Is there a way to troubleshoot
I have a set of passwordless-ssh nodes, each node can ssh into any other.,
for h1 in A B C D; do for h2 in A B C D; do ssh $h1 ssh $h2 hostname; done;
Generally tree spawn works, however there is one host where
launching mpirun with tree spawn hangs as soon as there are 6 or more host
(with launch node also in the host list). If the launcher is not in the
host list the hang happens with five hosts.