Add support for persistent disks in the hydra iso.

nix/configuration/hosts/hydra/default.nix

@@ -1,9 +1,31 @@
-{ config, pkgs, ... }:
+#
+# Testing:
+# doas "$(nix-build '<nixpkgs>' --no-out-link -A 'qemu')/bin/qemu-system-x86_64" \
+#      -accel kvm \
+#      -cpu host \
+#      -smp cores=8 \
+#      -m 32768 \
+#      -drive "file=$(nix-build '<nixpkgs>' --no-out-link -A 'OVMF.fd')/FV/OVMF.fd,if=pflash,format=raw,readonly=on" \
+#      -drive file=/tmp/localdisk.img,if=none,id=nvm,format=raw \
+#      -device nvme,serial=deadbeef,drive=nvm \
+#      -nic user,hostfwd=tcp::60022-:22 \
+#      -boot order=d \
+#      -cdrom "$(readlink -f /persist/machine_setup/nix/configuration/result/iso/nixos*.iso)" \
+#      -display vnc=127.0.0.1:0
+#
+
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
 {
   imports = [
-    ./hardware-configuration.nix
     ./disk-config.nix
+    ./hardware-configuration.nix
     ./optimized_build.nix
+    ./vm_disk.nix
   ];
 
   # Generate with `head -c4 /dev/urandom | od -A none -t x4`
@@ -21,9 +43,10 @@
 
   me.emacs_flavor = "plainmacs";
   me.graphical = false;
-  me.zsh.enable = true;
+  me.vm_disk.enable = true;
   me.wireguard.activated = [ ];
   me.wireguard.deactivated = [ ];
+  me.zsh.enable = true;
 
   # Trust this key so nix running as root can ssh into hydra.
   users.users.talexander.openssh.authorizedKeys.keys = [