test: update test-net-connect-handle-econnrefused

* var -> const
* assert.equal() -> assert.strictEqual()
* assert.ok(false) -> common.fail()

PR-URL: https://github.com/nodejs/node/pull/9932


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