MockedStreams takes the Stream properties way too literally

If you pass in the classOf the log and continue exception handler, the mocked streams fails because it can't cast this to a string. KafkaStreams takes care of this internally. 

```
p.put(DEFAULT_DESERIALIZATION_EXCEPTION_HANDLER_CLASS_CONFIG,
      classOf[LogAndContinueExceptionHandler])
```

KafkaStream's Properties is a Hashtable<Object, Object>

This is with version 3.4.0