Add support for ed25519 keys

[meling]

Currently, it seems iago only supports rsa keys, resulting in the following error:

ssh: handshake failed: knownhosts: key mismatch

We should support also ed25519 keys.

[meling]

It turns out this isn't related to the user's registered public key in the authorized_keys file.

The issue occurs if you do not manually log into each host but run a script like this:

#!/bin/bash
for i in {2..30} ; do
  ssh -o PreferredAuthentications=publickey -o StrictHostKeyChecking=no bbchain$i echo "hello bbchain$i"
done

To avoid having to "approve" the host's key. The above script only adds one of the host's public keys to the known_hosts file, and this may not be the one used by the underlying ssh handshake procedure.

The workaround is to fix the script to update all the host keys on your machine so that the handshake can use one of the other host keys available. Currently, rsa-based and ecdsa-based host keys seem to work.

#!/bin/bash
for i in {2..30} ; do
  ssh -o UpdateHostKeys=yes -o PreferredAuthentications=publickey -o StrictHostKeyChecking=no bbchain$i echo "hello bbchain$i"
done

We need to figure out how to configure the handshake procedure to support ed25519 host keys.