[Ndiff] Fix DeprecationWarning under python -3

Classes that inherit __hash__ and comparison functions like __eq__ (e.g.
from object) but only override one of them will break under Python 3.
This is because a class shouldn't use one criterion for equality and a
different one for hashing. Explicitly discarding the inherited __hash__
method disables this warning and makes the class unhashable (not a
problem in this case).

ndiff/ndiff.py

@@ -330,6 +330,7 @@ class Service(object):
         # self.ostype = None
         # self.devicetype = None
 
+    __hash__ = None
     def __eq__(self, other):
         return self.name == other.name \
             and self.product == other.product \
@@ -383,6 +384,7 @@ class ScriptResult(object):
         self.id = None
         self.output = None
 
+    __hash__ = None
     def __eq__(self, other):
         return self.id == other.id and self.output == other.output