Change legacy `menu.lst` location

- Make a `/boot/grub/grub.conf` and symlink to that
- Might be better when system updates, or so says
  http://wiki.xen.org/wiki/PvGrub#Install_a_stub_grub.conf_in_the_guest_so_that_the_grub_update_scripts_won.E2.80.99t_fail
  (we're not using pv-grub but the same concept applies)