I had this problem earlier as well. What I did was after booting with the ISO, I set a new password for the rancher user like so:
[rancher@rancher ~]$ sudo passwd rancher
Changing password for rancher
New password:
This allowed me to scp my local copy of cloud-config.yml over to the rancher machine before proceeding with bare metal installation as per the docs. You might want to also run your cloud-config.yml through a YAML validator just to ensure it’s working. Hope this helps.
-najib