test: refactor test-http-dns-fail

* remove counter used to control function execution
* use commont.mustCall to control the function execution
* use const and let instead of var
* use arrow functions

PR-URL: https://github.com/nodejs/node/pull/10243


Reviewed-By: Italo A. Casas <me@italoacasas.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Lance Ball <lball@redhat.com>
Reviewed-By: Brian White <mscdex@mscdex.net>