Record the stack trace for current thread in FutureUtils.get

This is for debugging. As in async client, the retry will be done in the retry timer thread, so the exception we get from the CompletableFuture will have a stack trace starting from the root of the retry timer. If we just throw this exception out when calling future.get(by unwrapping the ExecutionException), the upper layer even can not know where is the exception thrown...

This happens for me many times, so I propose that we always create a new exception in FutureUtils.get, so at least we can record the stack trace for the method calling FutureUtils.get...