test: cleanup test-stdout-close-catch.js

Added common.mustCall in child process on 'close' callback
Changed several 'var' statements to 'const' or 'let' where appropriate
Also linting

PR-URL: https://github.com/nodejs/node/pull/10006


Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>