virtualisation/vagrant-virtualbox: use system.build.image

nixos/modules/virtualisation/vagrant-virtualbox-image.nix

@@ -1,6 +1,6 @@
 # Vagrant + VirtualBox
 
-{ config, pkgs, ... }:
+{ config, pkgs, lib, ... }:
 
 {
   imports = [
@@ -22,8 +22,11 @@
 
   # generate the box v1 format which is much easier to generate
   # https://www.vagrantup.com/docs/boxes/format.html
+  image.extension = lib.mkOverride 999 "${config.image.baseName}.box";
+  system.nixos.tags = [ "vagrant"];
+  system.build.image = lib.mkOverride 999 config.system.build.vagrantVirtualbox;
   system.build.vagrantVirtualbox = pkgs.runCommand
-    "virtualbox-vagrant.box"
+    config.image.fileName
     {}
     ''
       mkdir workdir