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

scripts/slave/recipes/skia/swarm_trigger.expected/No_downloaded_SKP_VERSION.json

 [
   {
     "cmd": [
       "git",
       "remote",
       "set-url",
       "origin",
       "https://skia.googlesource.com/skia.git"
     ],
     "cwd": "[SLAVE_BUILD]/skia",
@@ skipping 275 matching lines @@
       "0"
     ],
     "name": "Copy Go binary"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::gsutil]/resources/gsutil_wrapper.py",
       "--",
-      "[DEPOT_TOOLS]/gsutil.py",
+      "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "----",
       "help"
     ],
     "name": "gsutil help"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
@@ skipping 448 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",
       "-R",
       "gs://chromium-skia-gm/playback_42/skps/*",
       "[SLAVE_BUILD]/skps"
     ],
     "env": {
       "AWS_CREDENTIAL_FILE": "[HOME]/chromium-skia-gm.boto",
       "BOTO_CONFIG": "[HOME]/chromium-skia-gm.boto"
     },
@@ skipping 587 matching lines @@
       "@@@STEP_LOG_END@json.output@@@",
       "@@@STEP_LINK@shard #0 isolated out@blah@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]