During the exponential backoff waiting for the machine to be fully up
and running, also make sure that SSH is ready. The systemd dependencies
of the ready.service include the sshd.service among others but that is
not enough.
Other CoreOS users reported the same issue on IRC, so I feel fairly
confident to use the pragmatic approach of making sure SSH works on the
client side. #17403 is quite old and there are other pressing machine
issues that need attention.
[NO NEW TESTS NEEDED]
Fixes: #17403
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>