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# Type of request: This is a ...

[x] bug report
[ ] feature request

# Detailed description

In the `ReceiveMessageResult` of the SQS service, I saw this XML from localstack:

```
...
<MessageAttribute>
     <Name>encoding</Name>
    <Value>
        <DataType>String</DataType>
        <StringValue><![CDATA[gzip]]></StringValue>
    </Value>
</MessageAttribute>
...
```

The `<![CDATA[gzip]]>` is slightly different from AWS, which doesn't wrap the value in a `<!CDATA[[]]>` section. This shouldn't be a problem for XML parsers that accept both plain characters and CDATA sections for this element, but the XML parser I was using did not, which causes an error when running the code against localstack but not when running the code against AWS. There is obviously a bug in the XML parser as well, but I thought that I should at least post this here since it is different than what AWS SQS does.

## Expected behavior

MessageAttribute::Value elements should not be wrapped in `CDATA` sections.

## Actual behavior

MessageAttribute::Value elements all seem to be wrapped in `CDATA` sections.

# Steps to reproduce

Send a message to the SQS service which contains some custom message attributes, then make a ReceiveMessageRequest.

## Command used to start LocalStack

`docker run --env "SERVICES=sqs" localstack/localstack`

## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)

...

try:
                    result = self._execute(func_arn, func_details, event, context, version)
                except Exception as e:
                    raised_error = e
                    if asynchronous:
                        if get_from_event(event, 'eventSource') == EVENT_SOURCE_SQS:
                            sqs_queue_arn = get_from_event(event, 'eventSourceARN')
                            if sqs_queue_arn:
                                
                                dlq_sent = sqs_error_to_dead_letter_queue(sqs_queue_arn, event, e)
                        else:
                            
                            lambda_error_to_dead_letter_queue(func_details, event, e)
                    raise e
                finally:
                    self.function_invoke_times[func_arn] = invocation_time
                    callback and callback(result, func_arn, event, error=raised_error, dlq_sent=dlq_sent)
                
                return result
            return _run(func_arn=func_arn)
        
        if asynchronous:
            LOG.debug('Lambda executed in Event (asynchronous) mode, no response will be returned to caller')
            FuncThread(do_execute).start()
            return None, 'Lambda executed asynchronously.'
        return do_execute()
    def _execute(self, func_arn, func_details, event, context=None, version=None):
        """ This method must be overwritten by subclasses. """
        raise Exception('Not implemented.')
    def startup(self):