test: cleanup test-net-server-address.js

Refactored test:
- 'var' to 'const'
- functon to arrow function
- using common.mustCall() and common.fail()

PR-URL: https://github.com/nodejs/node/pull/8586


Reviewed-By: Yosuke Furukawa <yosuke.furukawa@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>
Reviewed-By: James M Snell <jasnell@gmail.com>