zdtm: lock can belong to child or parent

Locks created by flock() are associated with an open file description
This means that duplicate file descriptors (created by, for  example,
fork or  dup)  refer  to  the  same  lock.

Reported-by: Mr Jenkins
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>