v2022 ← v2023dev1 backport: lib: Manually unmount /boot before board reset

Backport of !35 (merged)

When preparing the OSTree commit to test the offline upgrade, i.e. creating an older commit based on the original one, rebooting on this old commit to remove the original one before rebooting again, the reboot is performed by Lava by reseting the board.
This currently end up by entries in /boot/lost+found meaning that the /boot partition was not clean at reset time and breaking files in it.

Workaround: manually unmount the boot partition before the board is reset by Lava to prevent unexpected entries in /boot/lost+found which can prevent subsequent boots.

https://phabricator.apertis.org/T8454

Signed-off-by: Frédéric Danis frederic.danis@collabora.com