Ssh retry

Hi,
In case the ssh port is already reachable --- e.g. via the wait_for construct --- but user's public key not yet being in place, it makes sense to give the ssh connection another chance. This is the case especially in EC2 while creating a new instance. Here, a booted instance undergoes some cloud-init tuning even though the sshd service is already running. Therefore, I'd like to propose following patch.

Thanks!