finalize cgroups correctly

We need to finalize the cg yard both on successful cgroup restore and on a
failed restore. Further, we should restore the cgroup properties before
allowing the task to continue in all modes (previously properties were only
restored correctly in --restore-detached mode).

CC: Saied Kazemi <saied@google.com>
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>