Use always_run v can_fail_build

scripts/slave/recipe_api.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import functools
 import imp
 import inspect
 import os
 import sys
 import tempfile
 
 
+class RecipeAbort(Exception):
+  pass
+
+
 class Placeholder(object):
   """Base class for json placeholders. Do not use directly."""
   def render(self, test_data):  # pragma: no cover
     """Return [cmd items]*"""
     raise NotImplementedError
 
   def step_finished(self, presentation, step_result, test_data):
     """Called after step completion. Intended to modify step_result."""
     pass
 
@@ skipping 284 matching lines @@
       if pre:
         old_followup(step_result)
         f(step_result)
       else:
         f(step_result)
         old_followup(step_result)
     if old_followup is not null_fn:
       _inner.__name__ += '[%s]' % old_followup.__name__
     return _inner
   return decorator