tests: add buildwmwithbootloader stub

tests/buildvmwithbootloader/build-vm.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+set -x
+rm *.qcow2
+rm result*
+set -e
+
+BUILD_NIXPKGS="${BUILD_NIXPKGS:-${HOME}/src/github/NixOS/nixpkgs.dev}"
+NIXOS_CONFIG="${NIXOS_CONFIG_OVERRIDE:-${PWD}/configuration.nix}"
+
+nix-build -K --show-trace build-vm.nix \
+    --arg vmPkgsPath '<nixos-18.03>' \
+    --argstr buildPkgsPath "${BUILD_NIXPKGS}" \
+    --argstr nixosConfigPath "${NIXOS_CONFIG}" \
+    -A vmWithBootLoaderMixed
+
+./result/bin/run-*-vm