test: refactor test-file-*

* var to const
* add check that expected error is ENOENT
* indexOf() to includes()

PR-URL: https://github.com/nodejs/node/pull/8999


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>