expand-on-first-boot: Additional findings

["Schmidl, Tobias" <tobiasschmidl@siemens.com>]

Hi all,

in addition to the changes in the last patch [1] I tried defer the call to
systemd-growfs to the way it was intended by systemd: By setting a fstab
option. This proved to be unsuccessful, as systemd-growfs ist triggered
via systemd-remount, and this is way earlier in the boot chain than I was
able to set expand-on-first-boot. (systemd-analyze seems to report not the
full truth in this case.) The same is with systemd-repart.

Additionally, systemd-repart requires the user to make changes (and, more
importantly, keep them in sync) to both the wic file and the systemd-
repart config file:
- The wic file needs to set the correct UUID for the partition - which are
  both platform and usage dependent, according to the Discoverable
  Partitions Specification [2]
- The systemd-config refers to these UUIDs in an abstracted way [3]

This is in my opinion too error prone to be used in a production
environment.

Kind regards,

Tobias

[1] https://groups.google.com/g/isar-users/c/8NATfl5i2a4
[2] https://systemd.io/DISCOVERABLE_PARTITIONS/
[3] https://manpages.debian.org/testing/systemd/repart.d.5.en.html