test: refactor test-async-wrap-*

* `assert.equal()` -> `assert.strictEqual()`
* add duration to `setTimeout()`

PR-URL: https://github.com/nodejs/node/pull/9663


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Prince John Wesley <princejohnwesley@gmail.com>