Fix parsing of default params and body params

- query_string_normalizer method is called multiple times from
  request.rb
- When it is called for default_params, we have to return the
  query_string in key=val format.
- When it is passed for body params which include a file, we need to
  send back the overridden way of [[key,val]] format.
- This difference makes sure that with default params, query string is
  generated properly and if the file params are present, body is
  generated properly.