Resync file owner if there are any discrepancies after the system is
upgraded from a different build system.
The script is to iterate all the files except /sysroot in parallel to
check for a change in the uid/gid post-upgrade. If there is
any it will trigger chown/chgrp to sync them according to the new
uid/gid. The script caches the unchanged uid/gid to skip files with
unchanged pairs and optimize the execution time. The scripts run via a
systemd unit which in turn requires ostree-finalized-stage.service
to ensure that the sync script runs only when a system is upgraded.
saypaul