The occasional failures of the RAID smoketest can be traced to a reliance on the disk name (/dev/sda, /dev/sdb) when flipping the boot order during the test. Caution against this assumption is mentioned here:
https://www.debian.org/releases/bullseye/amd64/release-notes/ch-information.en.html#scsi-non-deterministic

Add a utils function to get device name from the drive id specified in the qemu command and extend op-mode format_disk.py and raid.py to use id.