cg: Add rollback for add_cgroup

If add_cgroup_properties failed we have @ncd sitting
in @match->children or @current_controller->heads
list, and then we free @ncd entry leaving those
lists carrying dead pointers.

Add proper rollback action.

Signed-off-by: Cyrill Gorcunov <gorcunov@virtuozzo.com>
Acked-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>