With the update of systemd to v255, the repart tool switched to use 4K
sector sizes by default. This change sets the appliance-repart-image
test to use a sector size of 512B to fit in with the existing NixOS VM
test infrastructure using qemu disks with 512B sector sizes.
The version option is needed if you want to implement partition &
systemd-boot based A/B booting where the version information is encoded
in the files on the ESP. See systemd-sysupate docs for more details on
this:
https://www.freedesktop.org/software/systemd/man/latest/sysupdate.d.html
Note, however, that this is not *only* useful for systemd-sysupdate but
also for other similar updating tools/mechanisms.
