gsutil: use depot_tools.gsutil_py_path instead of path['depot_tools']

scripts/slave/recipes/cronet.expected/cronet_try.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport os, sys\n\nbuild_path = sys.argv[1]\nif os.path.exists(build_path):\n  for (path, dir, files) in os.walk(build_path):\n    for cur_file in files:\n      if cur_file.endswith('index.lock'):\n        path_to_file = os.path.join(path, cur_file)\n        print 'deleting %s' % path_to_file\n        os.remove(path_to_file)\n",
       "[SLAVE_BUILD]"
     ],
     "name": "cleanup index.lock",
     "~followup_annotations": [
@@ skipping 504 matching lines @@
       "[SLAVE_BUILD]/src/out/logcat"
     ],
     "name": "logcat_dump"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::gsutil]/resources/gsutil_wrapper.py",
       "--",
-      "[DEPOT_TOOLS]/gsutil.py",
+      "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "--force-version",
       "4.7",
       "-o",
       "GSUtil:parallel_composite_upload_threshold=50M",
       "----",
       "cp",
       "-a",
       "public-read",
       "[SLAVE_BUILD]/src/out/Debug/full_log",
       "gs://chromium-android/logcat_dumps/android_cronet_tester/571"
@@ skipping 50 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  os.remove(report)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]