rename ova (keep name 'exam' from pycourse repo)

flake.nix

@@ -79,8 +79,9 @@
       ova = (vm [
         (nixpkgs + "/nixos/modules/virtualisation/virtualbox-image.nix")
         {
+          # TODO is it possible to disable soundcard / usb here?
           virtualbox = rec {
-            vmName = "mop";
+            vmName = "exam";
             vmDerivationName = "${vmName}.vbox";
             vmFileName = "${vmName}.ova";
             memorySize = 2048;