build:wafsamba: Waf 1.8 compatible declaration of 'mandatory' configuration tests

build:wafsamba: Waf 1.8 compatible declaration of 'mandatory' configuration tests

The configuration tests raise exceptions by default in later Waf versions,
but the samba tests do not specify whether the errors should be raised or
not. This changes lifts the ambiguity.

Signed-off-by: Thomas Nagy <tnagy@waf.io>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Michael Adam <obnox@samba.org>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Mon Nov 16 14:50:39 CET 2015 on sn-devel-104