ctdb-locking: Reset real-time priority in lock helper

ctdb-locking: Reset real-time priority in lock helper

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12392

Earlier we were relying on SCHED_RESET_ON_FORK to reset the priority of lock
helper processes.  Since SCHED_RESET_ON_FORK support has been removed, the
scheduling priority of child processes created using vfork() need to be reset
explicitly in the helper processes.

Signed-off-by: Amitay Isaacs <amitay@gmail.com>
Reviewed-by: Martin Schwenke <martin@meltin.net>
Autobuild-User(master): Martin Schwenke <martins@samba.org>
Autobuild-Date(master): Fri Nov 18 10:18:27 CET 2016 on sn-devel-144