Py3 fixes for layer_model_helper.py (pytorch#10525)

Summary:
Fixes `__getattr__` to adhere to its Python API contract, and wraps `range()` call in a list since it does not return one anymore in Python 3.
Pull Request resolved: pytorch#10525

Reviewed By: ezyang

Differential Revision: D9441360

Pulled By: tomdz

fbshipit-source-id: d489c0e7cefecc4699ca866fd55ddbfa629688d4

Author: tomdz

caffe2/python/layer_model_helper.py

@@ -529,7 +529,7 @@ def apply_operator(net, in_record, out_record, **kwargs):
                 return self.add_layer(new_layer)
             return wrapper
         else:
-            raise ValueError(
+            raise AttributeError(
                 "Trying to create non-registered layer: {}".format(layer))
 
     @property
@@ -651,5 +651,5 @@ def breakdown_map(self, breakdown_map):
         # and change the assertion accordingly
         assert isinstance(breakdown_map, dict)
         assert all(isinstance(k, six.string_types) for k in breakdown_map)
-        assert sorted(list(breakdown_map.values())) == range(len(breakdown_map))
+        assert sorted(breakdown_map.values()) == list(range(len(breakdown_map)))
         self._breakdown_map = breakdown_map