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

scripts/slave/recipes/chromium_codesearch.expected/full_ChromiumOS_Codesearch_fail.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "chromium.infra.cron",
       "--builder",
       "ChromiumOS Codesearch",
@@ skipping 302 matching lines @@
       "[SLAVE_BUILD]/src/out/Debug/index_pack_chromeos.zip"
     ],
     "name": "create index pack"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::gsutil]/resources/gsutil_wrapper.py",
       "--",
-      "[DEPOT_TOOLS]/gsutil.py",
+      "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "----",
       "cp",
       "[SLAVE_BUILD]/src/out/Debug/index_pack_chromeos.zip",
       "gs://chrome-codesearch/prod/index_pack_chromeos_170242.zip"
     ],
     "name": "gsutil upload index pack",
     "~followup_annotations": [
       "@@@STEP_LINK@gsutil.upload@https://storage.cloud.google.com/chrome-codesearch/prod/index_pack_chromeos_170242.zip@@@"
     ]
   },
@@ skipping 10 matching lines @@
       "chromium_src_chromeos.tar.bz2"
     ],
     "name": "archive source"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::gsutil]/resources/gsutil_wrapper.py",
       "--",
-      "[DEPOT_TOOLS]/gsutil.py",
+      "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "----",
       "cp",
       "[SLAVE_BUILD]/chromium_src_chromeos.tar.bz2",
       "gs://chrome-codesearch/prod/chromium_src_chromeos_170242.tar.bz2"
     ],
     "name": "gsutil upload source tarball",
     "~followup_annotations": [
       "@@@STEP_LINK@gsutil.upload@https://storage.cloud.google.com/chrome-codesearch/prod/chromium_src_chromeos_170242.tar.bz2@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]