Retry if the future itself fails

I often get bitten by the fact that the retry logic will not retry if an exception gets thrown within the body of the future. The workaround I have been using in the past is to have the future wrap a `scala.util.Try`. Doing so works, but is unnecessary since `Try` is already incorporated into `scala.concurrent.Future` (see `Future.onComplete`, for instance). So having to deal with a `Future[Try[T]]` is a little redundant and unnecessarily cumbersome. 

As a solution, I added a simple `recoverWith` block that will perform a retry (and decrement the max retries) if the future fails. I also added a unit test