test: refactor test for net listen on fd0

Replace var to const/let, use common.mustCall on callbacks and move
process.on('exit') to the .on('error') handler

PR-URL: https://github.com/nodejs/node/pull/10025


Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>