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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)

...

lambda_client.create_event_source_mapping(
            EventSourceArn=queue_arn,
            FunctionName=function_name
        )
        rs = self.client.send_message(
            QueueUrl=queue_url,
            MessageBody='hello world.',
            DelaySeconds=delay_time
        )
        message_id = rs['MessageId']
        logs = aws_stack.connect_to_service('logs')
        time.sleep(delay_time / 2)
        
        rs = logs.describe_log_groups()
        self.assertEqual(
            len([lg['logGroupName']
                 for lg in rs['logGroups'] if lg['logGroupName'] == get_lambda_log_group_name(function_name)]),
            0
        )
        
        events = get_lambda_log_events(function_name, delay_time * 1.5)
        
        self.assertEqual(len(events), 1)
        message = events[0]['Records'][0]
        self.assertEqual(message['eventSourceARN'], queue_arn)
        self.assertEqual(message['messageId'], message_id)
        
        self.client.delete_queue(QueueUrl=queue_url)
        lambda_client.delete_function(FunctionName=function_name)
    def test_get_queue_attributes(self):