SQSMessageConsumer doesn't handle errors gracefully

Hi

`SQSMessageConsumer` has a tight loop in `poll()`, summarised as:

```
for (;;) {
try {
// receive a message
} catch (Exception e) {
exceptionHandler.accept(e);
}
}
```
When an exception occurs (for example, kill network connectivity for a `java.net.UnknownHostException: sqs.eu-west-1.amazonaws.com`), this spins away and generates a huge stack trace every few milliseconds, and consumes all CPU resources very quickly.

Please consider sleeping a second upon exception.

Thanks