Add _convert_model method

Author: Mike Kistler

watson_developer_cloud/watson_service.py

@@ -182,6 +182,12 @@ def unpack_id(dictionary, label_id):
             return dictionary[label_id]
         return dictionary
 
+    @staticmethod
+    def _convert_model(val):
+        if hasattr(val, "_to_dict"):
+            return val._to_dict()
+        return val
+
     @staticmethod
     def _get_error_message(response):
         """