The quick installer will ask you for the user you want to use (eg: root) every time it is run, even though the config yaml already has the user after the first run. It appears the file isn't checked until after the user is specified.
This prevents the quick installer from being run un-attended.
This should be fixed in recent puddles.
Verify this bug with atomic-openshift-utils-3.0.12-1.git.0.4c09c5b.el7aos.noarch. When "ansible_ssh_user: root" configured in the installer.cfg.yml, run atomic-openshift-installer with --unattended, it wouldn't ask user for the ansible_ssh_user anymore.