test: refactor the code in test-http-connect

* use common.mustCall to control the functions execution automatically
* use let and const instead of var
* use assert.strictEqual instead of assert.equal
* use arrow functions
* remove console.error and unnecessary variables

PR-URL: https://github.com/nodejs/node/pull/10397


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>