Simplify local grid hardware

As preparation for #87 (closed), I wanted to simplify the existing vagrant-related nix configuration.

The main changes are:

• Move the the configuration from hardware-virtual.nix to hardware-vagrant.nix.
• Remove the vagrant-guest.nix in favour of the upstream one. I'm guess the one we have was originally based on code from here, which is where are vagrant images are built from. The differences this seems to make are:
  • Details of sudoers file, most of which are duplicates, and the rest are some details of what environment variables can be passed..
  • jq and gnumake are not on the system path.
  • vagrant user is in group users instead of vagrant.
• Make publicIPv4 a NixOS option, rather than an argument.