The first thing I see is that the host key is not in the /root/.ssh/known_hosts file. Manually, from the root account on each compute node, you will need to ssh to every other node once to answer the validate host prompt.
Also, you will need to create an ssh key, without passphrase, in the root account of each compute node and copy the public key to every other compute node in the /root/.ssh/authorized_keys file