Added build watch for e2e tests

As a follow up from #323 I've added build watch, I'm looking for you comments @bparees @ironcladlou 
I really do want to not care... but I'm still really paranoid about introducing more complexity into the e2e scaffolding. I feel like we have a very tenuous grasp on stability right now, and the polling solution is seems much simpler (and thus probably less bug prone). That's not a knock on your impl, @soltysh, I think it's just the incidental complexity of working with bash in this context. I'm sorry to backpedal on this given it was my idea. :sweat:

I said my piece, majority shall rule!