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 
for key, subscriptions in SNS_SUBSCRIPTIONS.items():
        for sub in subscriptions:
            if sub['SubscriptionArn'] == sub_arn:
                return sub
def make_response(op_name, content=''):
    response = Response()
    if not content:
        content = '<MessageId>%s</MessageId>' % short_uid()
    response._content = """<{op_name}Response xmlns="http://sns.amazonaws.com/doc/2010-03-31/">
        <{op_name}Result>
            {content}
        </{op_name}Result>
        <ResponseMetadata><RequestId>{req_id}</RequestId></ResponseMetadata>
        </{op_name}Response>""".format(op_name=op_name, content=content, req_id=short_uid())
    response.status_code = 200
    return response
def make_error(message, code=400, code_string='InvalidParameter'):
    response = Response()
    response._content = """<ErrorResponse xmlns="http://sns.amazonaws.com/doc/2010-03-31/"><Error>
        <Type>Sender</Type>
        <Code>{code_string}</Code>
        <Message>{message}</Message>
        </Error><RequestId>{req_id}</RequestId>
        </ErrorResponse>""".format(message=message, code_string=code_string, req_id=short_uid())
    response.status_code = code
    return response
def create_sns_message_body(subscriber, req_data):