Fixed RiakHttpTransport with non-ascii streams

- Encoded data that has octets outside the 128 byte range fail in
  python's httplib
- Using a bytearray for the message body causes the entire stream to be
  converted to a bytearray when a str object is added to it and the
  message is transported correctly
- Added two tests one with unicode data in a json object and one unicode
  data in a string