Move recipe engine to third_party/recipe_engine.

scripts/slave/recipe_modules/disk/api.py

 # Copyright 2015 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.
 
-from slave import recipe_api
+from recipe_engine import recipe_api
 
 
 class DiskApi(recipe_api.RecipeApi):
   """DiskApi contains helper functions for reading disk info."""
 
   def space_usage(
       self, path=None, warning_level=None, previous_result=None,
       can_fail_build=False, name=None, **kwargs):
     """Displays disk space usage.
 
@@ skipping 50 matching lines @@
       }
     except Exception as ex:
       # Do not fail entire build because of a disk space step failure.
       if step:
         step.presentation.logs['exception'] = ['%r' % ex]
         step.presentation.status = self.m.step.WARNING
       if can_fail_build:
         raise recipe_api.StepFailure('Could not get disk info: %s' % ex)
       return