Wait till the ssh daemon (presumably) located in cloud becomes responsive,
or until --timeout is reached.

At this moment, public key of the actual user (owner of ~/.ssh/config)
needs to be stored in authorized_keys on the HOST side.

With --print-user and --check-cloud-user, you can work-around the known
security measure like:

  Please login as the user "centos" rather than the user "root"
  Please login as the user "fedora" rather than the user "root"
  Please login as the user "cloud-user" rather than the user "root".