Hello,
I am working with a SNS to SQS project, in it we want to use the feature `RawMessageBody` when subscribing.
By looking into the code I found that the attributes are not persisted, for example `RawMessageBody` is always set to 'false'. Elsewhere in the code the parameters seems to be correctly used and send transform the message accordingly.

I created a PR fixing this : https://github.com/localstack/localstack/pull/1234
Thank you 
self.subscriber['RawMessageDelivery'] = 'true'
        action = {
            'Message': ['msg']
        }
        result = sns_listener.create_sns_message_body(self.subscriber, action)
        self.assertEqual(result, 'msg')
    def test_create_sns_message_body(self):
        action = {
            'Message': ['msg']
        }
        result_str = sns_listener.create_sns_message_body(self.subscriber, action)
        result = json.loads(result_str)
        try:
            uuid.UUID(result.pop('MessageId'))
        except KeyError:
            assert False, 'MessageId missing in SNS response message body'
        except ValueError:
            assert False, 'SNS response MessageId not a valid UUID'
        assert_equal(result, {'Message': 'msg', 'Type': 'Notification', 'TopicArn': 'arn'})