reinstall: Better UX for cloud-init images

[ckyrouac]

spawned from #1155 (comment)

• Detect when the target container image has cloud-init
• Skip the SSH key stuff then
• To be extra nice, we could also parse the cloud-init config and detect this case of going from RHEL-with-ec2-user to RHEL-with-cloud-user and print something very visible post-install
  ?