cg: restore special cpuset props only in cgs criu creates

Previously we were trying to copy the root cg properties recursively to attempt
to correct invalid restores. However, based on some ML discussion, we should
only restore exactly what was dumped. Users need to set up their cg heirarchies
correctly (that is, they should not set up any options in the parent that would
conflict with what was dumped) in order to restore successfully.

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>