Add a default DeletionPolicy for Fn::ResourceFacade

The provider template can't know whether this is explicitly included in the
facade resource's definition, and shouldn't need to.

Closes-bug: #1299202

Change-Id: I01177a84b86b69e221d83d87f3efd9e07e5b9c1f

heat/engine/cfn/functions.py

@@ -529,14 +529,7 @@ class ResourceFacade(function.Function):
         elif attr == self.UPDATE_POLICY:
             return self.stack.parent_resource.t.get(attr, {})
         elif attr == self.DELETION_POLICY:
-            try:
-                return self.stack.parent_resource.t[attr]
-            except KeyError:
-                # TODO(zaneb): This should have a default!
-                fmt_data = {'fn_name': self.fn_name,
-                            'key': attr}
-                raise KeyError(_('"%(fn_name)s" '
-                                 'key "%(key)s" not found') % fmt_data)
+            return self.stack.parent_resource.t.get(attr, 'Delete')
 
 
 def function_mapping(version_key, version):

heat/tests/test_parser.py

@@ -466,11 +466,7 @@ Mappings:
         stack = parser.Stack(self.ctx, 'test_stack',
                              parser.Template({}),
                              parent_resource=parent_resource)
-        error = self.assertRaises(KeyError,
-                                  self.resolve,
-                                  snippet,
-                                  stack.t, stack)
-        self.assertIn(snippet.keys()[0], str(error))
+        self.assertEqual('Delete', self.resolve(snippet, stack.t, stack))
 
     def test_prevent_parameters_access(self):
         expected_description = "This can be accessed"