<!-- Love localstack? Please consider supporting our collective:
👉  https://opencollective.com/localstack/donate -->

# 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)

...

while len(list_obj):
        del list_obj[0]
def cleanup_tmp_files():
    for tmp in TMP_FILES:
        try:
            rm_rf(tmp)
        except Exception:
            pass  
    del TMP_FILES[:]
def new_tmp_file():
    """ Return a path to a new temporary file. """
    tmp_file, tmp_path = tempfile.mkstemp()
    os.close(tmp_file)
    TMP_FILES.append(tmp_path)
    return tmp_path
def new_tmp_dir():
    folder = new_tmp_file()
    rm_rf(folder)
    mkdir(folder)
    return folder
def is_ip_address(addr):
    try:
        socket.inet_aton(addr)
        return True
    except socket.error:
        return False
def is_zip_file(content):
    stream = BytesIO(content)
    return zipfile.is_zipfile(stream)
def unzip(path, target_dir, overwrite=True):