[ http ] request method should handle 400...500 errors

[kilgore5]

need to make this error more understandable: https://github.com/kingandpartners/larsson_and_jennings/issues/597

Unauthorized response ends up with JSON::ParserError

need something like handle_response method in https://github.com/Shopify/active_utils/blob/master/lib/active_utils/posts_data.rb#L74

def handle_response(response)
      case response.code.to_i
      when 200...300
        response.body
      else
        raise ResponseError.new(response)
      end
    end