Do not restrict VMs to a single config

Also "allows" full-system build without install.

build_os.sh

@@ -0,0 +1,66 @@
+#!/usr/bin/env nix-shell
+#! nix-shell -i bash
+#! nix-shell -p bash nix-output-monitor
+
+set -euo pipefail
+SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
+
+# Parse arguments
+function help {
+    echo "Usage: $0 [-h|-v|-b] profile"
+    echo
+    echo "Arguments:"
+    echo "  profile: OS/disk profile to use"
+    echo
+    echo "Options:"
+    echo "  -h: Display this help message."
+    echo "  -v: Build a virtual machine."
+    echo "  -b: Build a virtual machine with boot loader."
+}
+
+attr=system
+while getopts "hvb" OPTION
+do
+    case "$OPTION" in
+        h)
+            help
+            exit 0
+            ;;
+        v)
+            attr=vm
+            ;;
+        b)
+            attr=vmWithBootLoader
+            ;;
+        ?)
+            help
+            exit 2
+            ;;
+    esac
+done
+shift "$(($OPTIND -1))"
+
+if [ "$#" -ne 1 ]
+then
+    help
+    exit 2
+fi
+profile="$1"
+
+profile_dir="${SCRIPT_DIR}/${profile}"
+if [ ! -d "$profile_dir" ]
+then
+    echo "Profile not found."
+fi
+
+nixos_config="${profile_dir}/os.nix"
+if [ ! -f "$nixos_config" ]
+then
+    echo "NixOS configuration not found."
+fi
+
+set -x
+
+nom-build '<nixpkgs/nixos>' -I "nixos-config=${nixos_config}" -A "$attr" -o "${profile_dir}/${attr}"
+
+echo