I highly advise not using pg_upgradecluster. It's a wrapper script for debian based systems and it obfuscates way too much of the upgrade process as you're seeing yourself with this question. You can use pg_createcluster to create the upgrade target version. Copy your config files over as needed but then just use pg_upgrade itself so it's clear what is getting upgraded and you'll get much better feedback about the process itself if there is a problem.
