s4-dsdb: instanceType NC_HEAD is only allowed combined with WRITE for an originating add operation

As described in MS-ATDS 3.1.1.5.2.8.

Signed-off-by: Nadezhda Ivanova <nivanova@symas.com>
Reviewed-by:   Andrew Bartlett <abartlet@samba.org>

Autobuild-User(master): Nadezhda Ivanova <nivanova@samba.org>
Autobuild-Date(master): Sun Nov  3 16:17:30 CET 2013 on sn-devel-104