The cloneConfig module can prevent the incus-create-nixos-config.service from
running because it will already have generated a configuration.nix.
Also modifies the test to hopefully catch that.
Fixes 0f363a1cb4
docker: move /init symlink creation from activationScript to installBootLoader,
which is the mechanism switch-to-configuration already uses for this purpose.
lxc: remove redundant activation script.
The installBootLoader hook was already handling /sbin/init.
incus: replace activationScript with a oneshot systemd service that uses
ConditionPathExists to create /etc/nixos/configuration.nix only on first
boot.
See: https://github.com/NixOS/nixpkgs/issues/475305