Conflicting cgroup usage with system manager #463

Cgroup management has been expected to follow some rules for some time now, especially on systemd systems:
https://www.freedesktop.org/wiki/Software/systemd/ControlGroupInterface/

This basically means that we have to ask for cgroup delegation and can then only manage processes under a specific subtree. A more concerning issue for LISA is that the freezer cgroup usage moves processes from wherever they were to a given cgroup, and then move them back to the root group. AFAIU this will break systemd pretty badly, as all tasks are in a specific group (slices/services) to start with, and not in root group.

Cgroup delegation would limit the use of the freezer to a subset of tasks, but services could be manually stopped to achieve similar effects.