Move recipe engine to third_party/recipe_engine.

scripts/slave/recipes/example/defer_multiple.py

 # Copyright 2014 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.
 
 DEPS = [
   'step',
   'example',
 ]
 
-from slave import recipe_api
+from recipe_engine import recipe_api
 
 @recipe_api.composite_step
 def deferrer(api):
   with api.step.defer_results():
     api.example('aggregated start')
     api.example('aggregated finish')
 
 def normal(api):
   api.example('normal start')
   api.example('normal finish')
@@ skipping 30 matching lines @@
 
   yield (
       api.test('nested_normal_fail') +
       api.step_data('normal start', retcode=1)
     )
 
   yield (
       api.test('nested_comp_fail') +
       api.step_data('composite start', retcode=1)
     )