CVE-2018-16852 dcerpc dnsserver: Verification tests

CVE-2018-16852 dcerpc dnsserver: Verification tests

Tests to verify
Bug 13669 - (CVE-2018-16852) NULL
            pointer de-reference in Samba AD DC DNS management

The presence of the ZONE_MASTER_SERVERS property or the
ZONE_SCAVENGING_SERVERS property in a zone record causes the server to
follow a null pointer and terminate.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13669

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>