Subiquity images mount /usr/lib/modules from a squashfs, which systemd
tries to unmount on shutdown, whilst they are still being in use. As
systemd-udevd kmod built-in's libkmod has modules.* files
memorymapped. This produces an warning on shutdown, flooding the
screen with messages as systemd switches to a more verbose
output. Specify LazyUnmount=yes on that mount, such that unmount call
succeeds without flooding the shutdown log.
ubuntu-cdimage/debian-cd/tools/add_live_filesystem helpfully adds a
'filesystem.' prefix to the squashfs, hence the name of the file
didn't match what's on disk.
