fix recipe_simulation recipe

scripts/slave/recipes/infra/recipe_simulation.py

 # Copyright 2016 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.
 """A continuous builder which runs recipe tests."""
 
 from recipe_engine.recipe_api import Property
 
 DEPS = [
   'depot_tools/bot_update',
   'depot_tools/gclient',
@@ skipping 12 matching lines @@
 
 def RunSteps(api, project_under_test):
   root_dir = api.path['slave_build']
   cache_dir = root_dir.join('_cache_dir')
 
   c = api.gclient.make_config(CACHE_DIR=cache_dir)
   soln = c.solutions.add()
   soln.name = project_under_test
   soln.url = api.luci_config.get_project_metadata(
       project_under_test)['repo_url']
+  soln.revision = 'HEAD'
 
   api.bot_update.ensure_checkout(
       force=True, gclient_config=c,
       cwd=root_dir)
 
   # TODO(martiniss): allow recipes.cfg patches to take affect
   # This requires getting the refs.cfg from luci_config, reading the local
   # patched version, etc.
   result = api.luci_config.get_project_config(project_under_test, 'recipes.cfg')
   recipes_cfg = api.luci_config.parse_textproto(result['content'].split('\n'))
@@ skipping 12 matching lines @@
           mastername='chromium.tools.build',
           buildername='recipe simulation tester',
           revision='deadbeaf',
           project_under_test='build',
       ) +
       api.luci_config.get_projects(('build',)) +
       api.luci_config.get_project_config(
           'build', 'recipes.cfg',
           'recipes_path: "foobar"')
   )