Bug#944389: lxc: Fails to work with cgroupv2 / unified hierarchy

[Ryutaroh Matsumoto]

Control: tags -1 + fixed

I made a user instruction on how to use lxc on a Debian host booted with
systemd.unified_cgroup_hierarchy=1 at
https://wiki.debian.org/LXC/CGroupV2
I believe that this issue is now resolved, but I refrain from closing this,
while I add "fixed" tag. Ryutaroh Matsumoto