Params normalization issue

- query_string_normalizer method is called multiple times from httparty/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.