fix recipe_simulation recipe

scripts/slave/recipes/infra/recipe_simulation.expected/normal.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/tools/pycurl.py",
       "https://luci-config.appspot.com/_ah/api/config/v1/projects",
       "--outfile",
       "/path/to/tmp/",
       "--attempts",
@@ skipping 16 matching lines @@
       "cache_dir = '[SLAVE_BUILD]/_cache_dir'\nsolutions = [{'deps_file': 'DEPS', 'managed': True, 'name': 'build', 'url': 'https://repo.repo/build'}]",
       "--root",
       "build",
       "--revision_mapping_file",
       "{}",
       "--git-cache-dir",
       "[SLAVE_BUILD]/_cache_dir",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
-      "build@deadbeaf",
+      "build@HEAD",
       "--force",
       "--output_manifest"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"did_run\": true, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"fixed_revisions\": {@@@",
-      "@@@STEP_LOG_LINE@json.output@    \"build\": \"deadbeaf\"@@@",
+      "@@@STEP_LOG_LINE@json.output@    \"build\": \"HEAD\"@@@",
       "@@@STEP_LOG_LINE@json.output@  }, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"manifest\": {}, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"patch_failure\": false, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"patch_root\": \"build\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"properties\": {}, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"root\": \"build\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"step_text\": \"Some step text\"@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
@@ skipping 18 matching lines @@
       "simulation_test"
     ],
     "name": "recipe simulation test"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]