Escape arguments when installer invokes commands

The usage of shell: true means that no escaping is done on the arguments
passed to the commands invoked by the installer. This leads to the
installation failing if the user for example puts a space in the
username for the admin account.

Fix by escaping the arguments passed on command lines. This is
unreasonably complicated on Windows 😡.

test/create/echo_args.js

@@ -0,0 +1,4 @@
+"use strict";
+if (module === require.main) {
+	process.stdout.write(JSON.stringify(process.argv.slice(2)));
+}