Ubuntu 16.04 - Disable the user list in gdm greeter

This is probably one of those common queries, but the solution I tried in 14.04 LTS now doesn't work in 16.04 !!

I have a netboot install of ubuntu, which adds ubuntu-gnome-desktop as the desktop environment. I want to prevent the user list from showing up on the login greeter, which was achieved in 14.04 by setting "greeter-hide-users=true" in an /etc/lightdm/lightdm.conf.d config file, and also setting "disable-user-list=true" in an /etc/dconf/db/gdm.d config file.

I guess one of those settings worked, because what I want is purely a prompt for the useame, with no indication of other users showing.

We're ruing NIS.

In 16.04, the same netboot config files have been migrated, and I can't use the same settings to disable the user list. I've tried all sorts of options, but none seem to work

My desktop is "ubuntu-gnome-desktop", ruing gdm3 with unity-greeter - fairly bog-standard.....

Can anyone help? Configuration settings would be useful, as I want to be able to configure the system during the network install, either via kickstart / preseed or during postinstall scripts.

Thanks in advance