Fix SSH polluting known_hosts

In case NoHostAuthenticationForLocalhost is not specified in user's SSH
configuration, starting the SSH daemon will write to the known_hosts
file, potentially leading to conflicts later when the same port is
reused.
Test the SSH connection with the option on, but without touching the
user's configuration.
Merge pull request #37 from koterpillar/fix-ssh-polluting-known-hosts

Fix SSH polluting known_hosts