installerIso attributes no longer (?) work if boot.loader.grub.enable is set

[sternenseemann]

> nix-instantiate -A machines.sternenseemann.ludwig.installerIso
error: The option `boot.loader.grub.enable' has conflicting definition values:
- In `/nix/var/nix/profiles/per-user/root/channels/vuizvui/nixpkgs/nixos/modules/installer/cd-dvd/iso-image.nix': false
- In `/home/lukas/src/nix/vuizvui/machines/sternenseemann/ludwig.nix': true
Use `lib.mkForce value` or `lib.mkDefault value` to change the priority on any of these definitions.

(use '--show-trace' to show detailed location information)

It appears that it fails while merging the machine config and the iso-image.nix module before there is an opportunity of the lib.mkForce in mkIso to kick in.

[sternenseemann]

Seems like in practice even more problems arise such as no-x-libs.nix conflicting with a lot of settings in normal machines. Maybe this idea doesn't work as well anymore or another nixos module should be used for the installer media.