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

scripts/slave/recipes/infra/recipe_autoroller_public.expected/nontrivial.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "config",
       "--spec",
       "cache_dir = '[GIT_CACHE]'\nsolutions = [{'deps_file': '.DEPS.git', 'managed': True, 'name': 'infra', 'url': 'https://chromium.googlesource.com/infra/infra.git'}]"
     ],
@@ skipping 297 matching lines @@
       "@@@STEP_LOG_LINE@output@+some other line@@@",
       "@@@STEP_LOG_END@output@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::gsutil]/resources/gsutil_wrapper.py",
       "--",
-      "[DEPOT_TOOLS]/gsutil.py",
+      "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "----",
       "cat",
       "gs://recipe-roller-cl-uploads/791ad91de804e9b08076c4db2081bfa6"
     ],
     "name": "build.gsutil cat",
     "stderr": "/path/to/tmp/",
     "stdout": "/path/to/tmp/",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LOG_LINE@stderr@Error: No URLs matched ...@@@",
@@ skipping 32 matching lines @@
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LINK@Issue 123456789@https://codereview.chromium.org/123456789@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::gsutil]/resources/gsutil_wrapper.py",
       "--",
-      "[DEPOT_TOOLS]/gsutil.py",
+      "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "----",
       "cp",
       "{\"diff_digest\": \"d4fbd1f86c94d02a0e9f2a3d08aebc1c\", \"issue\": \"123456789\", \"issue_url\": \"https://codereview.chromium.org/123456789\"}",
       "gs://recipe-roller-cl-uploads/791ad91de804e9b08076c4db2081bfa6"
     ],
     "name": "build.gsutil upload",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LINK@gsutil.upload@https://storage.cloud.google.com/recipe-roller-cl-uploads/791ad91de804e9b08076c4db2081bfa6@@@"
     ]
@@ skipping 13 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@shutil.rmtree(sys.argv[1])@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]