build: Fix cluster-support option, default was 'None' now 'False'

build: Fix cluster-support option, default was 'None' now 'False'

Cluster-support had some auto-detection but no longer does.

Prior to commit id(s) e67c4b977a52d1744f4da8296bbcd7c213cbe92a &
69c0c43d55c93b82b2e398d5c61009fd347170bf cluster support was auto
detected

Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Uri Simchoni <uri@samba.org>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
Autobuild-User(master): Amitay Isaacs <amitay@samba.org>
Autobuild-Date(master): Tue Feb 16 04:03:14 CET 2016 on sn-devel-144