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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)

...

body_key = 'MD5OfMessageBody' if outgoing else 'MD5OfBody'
            return set([
                (m[body_key], m['MD5OfMessageAttributes'])
                for m in messages
            ])
        messages_to_send = [
            {
                'Id': 'message{:02d}'.format(i),
                'MessageBody': 'msgBody{:02d}'.format(i),
                'MessageAttributes': {
                    'CustomAttribute': {
                        'DataType': 'String',
                        'StringValue': 'CustomAttributeValue{:02d}'.format(i)
                    }
                }
            }
            for i in range(1, 11)
        ]
        resp = self.client.send_message_batch(QueueUrl=queue_url, Entries=messages_to_send)
        sent_hashes = get_hashes(resp.get('Successful', []), outgoing=True)
        self.assertEqual(len(sent_hashes), len(messages_to_send))
        for i in range(2):
            messages = receive_messages(VisibilityTimeout=0)['Messages']
            received_hashes = get_hashes(messages)
            self.assertEqual(received_hashes, sent_hashes)
        self.client.delete_message_batch(
            QueueUrl=queue_url,
            Entries=[