Simplifies __ne__ in BaseModel

This change uses 'not __eq__' to implement __ne__ preventing
execeptions from being raised when obj passed in does not have
__dict__. Example are instances of tuple, string, int, float,
bool...

Change-Id: Idf82eeeb865a121d5c81c5654e7c21e71e555238

cafe/engine/models/base.py

@@ -141,13 +141,7 @@ class BaseModel(object):
         return False
 
     def __ne__(self, obj):
-        if obj is None:
-            return True
-
-        if vars(obj) == vars(self):
-            return False
-        else:
-            return True
+        return not self.__eq__(obj)
 
     def __str__(self):
         strng = '<{0} object> {1}'.format(