ABRoot fails to clean up

[taukakao]

When running any operation, ABRoot will fail to unmount some drives:

Partition.Unmount:info:running...
Partition.Unmount:err(1.000000):no such file or directory
Partition.Unmount:info:running...
Partition.Unmount:err(1.000000):device or resource busy
ABSystem.UnlockUpgrade:info:lock file removed

The things that are still mounted afterwards are:

/dev/mapper/vos--root-init on /tmp/tmp.XQjmqtY2KY type ext4 (rw,relatime)
/dev/mapper/vos--root-root--a on /part-future type btrfs (rw,relatime,ssd,discard=async,space_cache=v2,subvolid=5,subvol=/)
/dev/mapper/vos--var-var on /var/lib/abroot/storage/graph/overlay type btrfs (rw,relatime,ssd,discard=async,space_cache=v2,subvolid=597,subvol=/lib/abroot/storage)
/dev/mapper/vos--root-init on /part-future/.system/boot/init type ext4 (rw,relatime)

I think we should probably use "umount -R" or something similar in the cleanup to prevent any stray mounts from for example the chroot to prevent unmounting.