There might be several same terminals opened (say
tty6 or whatever) which gonna look as separate
files but actually pointing to the same tty kernel
instance. Moreover if it's a controlling terminal
we will be trying to restore it as many times as
find non zero sid on a peer.

Instead lets do a simple trick first: choose a leader
from a terminal group and use it only for controlling
terminal restoration.

https://jira.sw.ru/browse/PSBM-40969Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Reviewed-by: Andrew Vagin <avagin@odin.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>