container_add_task(): return an error from libcg

Instead of returning -1, return an actual error from libcgroup.
Note this return code is used that way in both calls to
container_add_task().

Cc: Glauber Costa <glommer@openvz.org>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
1 file changed