cgroups v2 support

[pboguslawski]

Ganeti (checked in Debian 9 and Debian 11) doesn't separate cgroups of guest processes from other heavy tasks like gnt-backups or wiping disks (backup restore/disk grow); systemd-cgls shows all processes under ganeti.service.

Consider using diffferent cgroups for VMs similar to
https://libvirt.org/cgroups.html

gnt-backups/wiping should also use separate cgroup from guest processes.

[saschalucas]

ATM Ganeti has no concepts for cgroups, it even still defaults to use sysv-init script wrapped in systemd-generator. This leads to various problems: i.e. crashed instances (re-)started by the ganeti-watcher belong to the cron service slice.

Any help with systemd enhancement is highly appreciated.