Bug#942230: fromiso on a multi-device btrfs needs btrfs device scan

[pk <pkoroau@gmail.com>]

Package: debian-live

Booting lxqt 10.1 live iso, stored on a multi-device btrfs, fails with
an infinite loop.

Workaround: boot with break, then:
modprobe btrfs
btrfs device scan
^D


In theory, another approach would be to pass the list of partitions as
a mount option, as done on installed distros that do not run the
device scan:
rootflags=device=/dev/sda2,...
However, this seems unapplicable to the boot parameter fromiso.