cgroup: Separate devices.list cgroup restoring

Now restore_special_property() only deals which special property
restore and restore_devices_list() deals with devices.list.

BTW, let's have two variables dev_allow and dev_deny on stack
to simplify it - all this fuss with old_val and old_name
kills the fun.

Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>