correctly handle async POST requests in swaggerpy + py3

[mxmul]

AsynchronousHTTPClient.start_request fails with a TypeError when the request has any form data in python3, because we assume that the body of the request is a byte string:

self = <class 'swaggerpy.async_http_client.AsynchronousHttpClient'>(), request_params = {'data': {'name': 'Matt'}, 'headers': {}, 'method': b'POST', 'url': 'http://localhost:49111/post'}

    def start_request(self, request_params):
        """Sets up the request params as per Twisted Agent needs.
            Sets up crochet and triggers the API request in background

            :param request_params: request parameters for API call
            :type request_params: dict

            :return: crochet EventualResult
            """

        prepared_request = requests.PreparedRequest()
        prepared_request.prepare(
            headers=request_params.get('headers'),
            data=request_params.get('data'),
            params=request_params.get('params'),
            files=request_params.get('files'),
            url=request_params.get('url'),
            method=request_params.get('method')
        )

        request_for_crochet = {
            'method': prepared_request.method or 'GET',
            'bodyProducer': FileBodyProducer(BytesIO(prepared_request.body))
>           if prepared_request.body else None,
            'headers': listify_headers(prepared_request.headers),
            'uri': prepared_request.url,
        }
E       TypeError: 'str' does not support the buffer interface

This branch encodes the request body to a byte string if it's unicode.

[coveralls]

Coverage decreased (-0.09%) to 93.404% when pulling da968ed on mxmul:mmulder_swaggerpy_py3_async_post into f4567a4 on Yelp:swaggerpy.

[coveralls]

Coverage decreased (-0.09%) to 93.404% when pulling da968ed on mxmul:mmulder_swaggerpy_py3_async_post into f4567a4 on Yelp:swaggerpy.

[prat0318]

👍 lgtm

[coveralls]

Coverage increased (+0.1%) to 93.602% when pulling a6f4c64 on mxmul:mmulder_swaggerpy_py3_async_post into f4567a4 on Yelp:swaggerpy.

[lucagiovagnoli]

If possible, I would suggest not using the AsynchronousHttpClient which comes with swaggerpy because I found it to be unstable on production. Also, swaggerpy in general as it is not actively maintained as bravado (and handles old swagger 1.x specs).