test: modernize JS and tighten equality checking

Node todo process example with the follow test-net-binary.js changes:

var --> const where applicable

==, assert.equal--> ===, assert.strictEqual for all cases

PR-URL: https://github.com/nodejs/node/pull/8476


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>