nixos/systemd-boot: Add basic test

nixos/modules/virtualisation/qemu-vm.nix

@@ -189,9 +189,18 @@ let
           mkdir /boot/grub
           echo '(hd0) /dev/vda' > /boot/grub/device.map
 
-          # Install GRUB and generate the GRUB boot menu.
-          touch /etc/NIXOS
+          # This is needed for systemd-boot to find ESP, and udev is not available here to create this
+          mkdir -p /dev/block
+          ln -s /dev/vda2 /dev/block/254:2
+
+          # Set up system profile (normally done by nixos-rebuild / nix-env --set)
           mkdir -p /nix/var/nix/profiles
+          ln -s ${config.system.build.toplevel} /nix/var/nix/profiles/system-1-link
+          ln -s /nix/var/nix/profiles/system-1-link /nix/var/nix/profiles/system
+
+          # Install bootloader
+          touch /etc/NIXOS
+          export NIXOS_INSTALL_BOOTLOADER=1
           ${config.system.build.toplevel}/bin/switch-to-configuration boot
 
           umount /boot