Currently we always create temporary directory where we restore
cgroups, but this won't work in case if mounting cgroups is forbidden
from inside of a container for some reason (as in OpenVZ kernel).

So one can pass --cgroup-yard option to specify an existing
directory where cgroups are living. By default we assume it
lays in /sys/fs/cgroup.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>