nixos: Give virtualbox-host.nix a better location.

In 14f09e0, I've introduced the module under modules/programs, because
the legacy virtualbox.nix was also under that path. But because we
already have modules/virtualisation/virtualbox-guest.nix, it really
makes sense to put this module alongside of it as well.

This module thus has no change in functionality and I've tested
evaluation against nixos/tests/virtualbox.nix and the manual.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

nixos/modules/module-list.nix

@@ -72,7 +72,6 @@
   ./programs/ssmtp.nix
   ./programs/uim.nix
   ./programs/venus.nix
-  ./programs/virtualbox-host.nix
   ./programs/wvdial.nix
   ./programs/freetds.nix
   ./programs/zsh/zsh.nix
@@ -486,6 +485,7 @@
   ./virtualisation/openvswitch.nix
   ./virtualisation/parallels-guest.nix
   ./virtualisation/virtualbox-guest.nix
+  ./virtualisation/virtualbox-host.nix
   ./virtualisation/vmware-guest.nix
   ./virtualisation/xen-dom0.nix
 ]