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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)

...

"Statement":[
    {
      "Effect": "Allow",
      "Principal": { "AWS": "*" },
      "Action": "sqs:SendMessage",
      "Resource": "'$sqs_queue_arn'",
      "Condition":{
        "ArnEquals":{
        "aws:SourceArn":"'$sns_topic_arn'"
        }
      }
    }
  ]
}
"""
THIS_FOLDER = os.path.dirname(os.path.realpath(__file__))
TEST_LAMBDA_ECHO_FILE = os.path.join(THIS_FOLDER, 'lambdas', 'lambda_echo.py')
TEST_MESSAGE_ATTRIBUTES = {
    'City': {
        'DataType': 'String',
        'StringValue': 'Any City'
    },
    'Population': {
        'DataType': 'Number',
        'StringValue': '1250800'
    }
}
class SQSTest(unittest.TestCase):
    @classmethod
    def setUpClass(cls):