Move recipe engine to third_party/recipe_engine.

scripts/slave/recipe_modules/step/example.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.
 
 DEPS = [
   'properties',
   'step',
 ]
 
-from slave import recipe_api
+from recipe_engine import recipe_api
 
 def GenSteps(api):
   # TODO(martinis) change this
   # The api.step object is directly callable.
   api.step('hello', ['echo', 'Hello World'])
   api.step('hello', ['echo', 'Why hello, there.'])
 
   # You can also manipulate various aspects of the step, such as env.
   # These are passed straight through to subprocess.Popen.
   # Also, abusing bash -c in this way is a TERRIBLE IDEA DON'T DO IT.
@@ skipping 69 matching lines @@
   yield (
       api.test('defer_results') +
       api.step_data('testa', retcode=1)
     )
 
   yield (
       api.test('infra_failure') +
       api.properties(raise_infra_failure=True) +
       api.step_data('cleanup', retcode=1)
     )