test: improve the code in test-pipe.js

* use const and let instead of var
* use common.mustCall to control functions executions
* use assert.strictEqual instead of assert.equal
* use assert.ifError to handle errors
* use arrow functions
* remove console.log and process.stdout.write

PR-URL: https://github.com/nodejs/node/pull/10452


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>