test: refactor cluster-net-listen-relative-path

Refactor test-cluster-net-listen-relative-path:

* Use arrow funcitons for callbacks.
* Move skip-test code closer to start of file.
* Use assert.ok() where appropriate.
* Capitalize and punctuate comments.

PR-URL: https://github.com/nodejs/node/pull/21863


Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>