juttle-engine-client watch doesn't work well on unix systems

[rlgomes]

Seems to detect the very first change and then stops after that, I did some quick debugging and figured its because the chokidar package is quite "buggy" and tries to massage some of the existing issues with using fs.watch and fs.watchFile but ultimately only works well on OSX. So I dug around a bit and there are some options to do polling which we could turn on and simply poll every second and it works perfectly fine on my system. I think we could detect the OS and take advantage of the non polling version on OSX while simply defaulting to polling every second on other systems doesn't seem like a horrible solution till chokidar or fs.watch becomes more reliable in the near future.