HttpServer wraps InterruptedExceptions by IOExceptions if interrupted in startup

Following on some discusson on mapred-dev, we should keep an eye on the fact that Jetty uses sleeps when starting up; jetty can be a big part of the delays of bringing up a node. When interrupted, the exception is wrapped by an IOException, the root cause is still there, just hidden.

If we want callers to distinguish InterruptedExceptions from IOEs, then this exception should be extracted. Some helper method to start an http daemon could do this -catch the IOE, and if there is a nested interrupted exception, rethrow it, otherwise rethrowing the original IOE