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

scripts/slave/recipe_modules/chromium_android/example.expected/perf_runner_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 498 matching lines @@
     "~followup_annotations": [
       "@@@STEP_TEXT@<br/>Device Affinity: 0<br/>@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::gsutil]/resources/gsutil_wrapper.py",
       "--",
-      "[DEPOT_TOOLS]/gsutil.py",
+      "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "----",
       "cp",
       "[TMP_BASE]/perf_archives_tmp_1/output_dir.zip",
       "gs://archives-bucket/perf_runner/perf_test.foo/20150928T110712_build_571.zip"
     ],
     "name": "gsutil upload perf_test.foo output dir archive",
     "~followup_annotations": [
       "@@@STEP_LINK@output_dir.zip@https://storage.cloud.google.com/archives-bucket/perf_runner/perf_test.foo/20150928T110712_build_571.zip@@@"
     ]
   },
@@ skipping 119 matching lines @@
       "PATH": "[SLAVE_BUILD]/src/third_party/android_tools/sdk/platform-tools:[SLAVE_BUILD]/src/build/android:%(PATH)s"
     },
     "name": "stack_tool_for_asan"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]