test: use Countdown in http test

PR-URL: https://github.com/nodejs/node/pull/17436


Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>