Revert "cgroups: Add ability to reuse existing cgroup yard directory"

Reasoning: some systems have /sys/fs/cgroup stuff mounted as read-only
and we have to either remount it rw or create our own set. The former
doesn't look sane as this rw remounting is also done by ststemd, so
let's return back to manual cgyard construction.

This reverts commit 860df95f.

Conflicts:
	cgroup.c
	include/cr_options.h

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>