<!-- 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)

...

return ContainerInfo(container_name, entry_point)
    def destroy_docker_container(self, func_arn):
        """
        Stops and/or removes a docker container for a specific lambda function ARN.
        :param func_arn: The ARN of the lambda function.
        :return: None
        """
        with self.docker_container_lock:
            status = self.get_docker_container_status(func_arn)
            docker_cmd = self._docker_cmd()
            
            container_name = self.get_container_name(func_arn)
            if status == 1:
                LOG.debug('Stopping container: %s' % container_name)
                cmd = (
                    '%s stop -t0 %s'
                ) % (docker_cmd, container_name)
                LOG.debug(cmd)
                run(cmd, asynchronous=False, stderr=subprocess.PIPE, outfile=subprocess.PIPE)
                status = self.get_docker_container_status(func_arn)
            if status == -1:
                LOG.debug('Removing container: %s' % container_name)
                cmd = (
                    '%s rm %s'
                ) % (docker_cmd, container_name)
                LOG.debug(cmd)
                run(cmd, asynchronous=False, stderr=subprocess.PIPE, outfile=subprocess.PIPE)
    def get_all_container_names(self):
        """
        Returns a list of container names for lambda containers.