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

scripts/slave/recipe_modules/chromium_android/example.expected/webview_cts_basic.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 156 matching lines @@
       "/path/to/tmp/"
     ],
     "name": "get version"
   },
   {
     "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",
       "----",
       "cp",
       "gs://build-bucket/build_product.zip",
       "[SLAVE_BUILD]/src/out/build_product.zip"
     ],
     "name": "gsutil download_build_product"
   },
   {
@@ skipping 508 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  os.makedirs(path, mode)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::gsutil]/resources/gsutil_wrapper.py",
       "--",
-      "[DEPOT_TOOLS]/gsutil.py",
+      "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "----",
       "cp",
       "gs://chromium-cts/android-cts-5.1_r5-linux_x86-arm.zip",
       "[BUILD]/site_config/cts/android-cts-5.1_r5-linux_x86-arm.zip"
     ],
     "name": "Update CTS.gsutil Download new CTS",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@"
     ]
   },
@@ skipping 36 matching lines @@
       "@@@STEP_LOG_LINE@disabled_tests@                          }@@@",
       "@@@STEP_LOG_END@disabled_tests@@@"
     ]
   },
   {
     "name": "$result",
     "reason": "Failed to parse the CTS output for the xml report file location",
     "status_code": 1
   }
 ]