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

scripts/slave/recipe_modules/amp/example.expected/split_example_basic.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::gsutil]/resources/gsutil_wrapper.py",
       "--",
-      "[DEPOT_TOOLS]/gsutil.py",
+      "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "----",
       "cp",
       "gs://chrome-amp-keys/main_pool/api_key",
       "[BUILD]/site_config/.amp_main_pool_key"
     ],
     "name": "gsutil download amp api key"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[build::gsutil]/resources/gsutil_wrapper.py",
       "--",
-      "[DEPOT_TOOLS]/gsutil.py",
+      "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "----",
       "cp",
       "gs://chrome-amp-keys/main_pool/api_secret",
       "[BUILD]/site_config/.amp_main_pool_secret"
     ],
     "name": "gsutil download amp api secret"
   },
   {
     "cmd": [
       "python",
@@ skipping 277 matching lines @@
     ],
     "name": "[upload logcat] unzip results for example_gtest_suite",
     "stdin": "{\"output\": \"[TMP_BASE]/amp_results_tmp_2/T35TRUN1D/unzipped_results\", \"zip_file\": \"[TMP_BASE]/amp_results_tmp_2/T35TRUN1D/results.zip\"}"
   },
   {
     "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]/amp_results_tmp_2/T35TRUN1D/unzipped_results/appurify_results/logcat.txt",
       "gs://chrome-amp-results/logcats/logcat_example_gtest_suite_T35TRUN1D.txt"
     ],
     "name": "gsutil [upload logcat] example_gtest_suite",
     "~followup_annotations": [
       "@@@STEP_LINK@logcat@https://storage.cloud.google.com/chrome-amp-results/logcats/logcat_example_gtest_suite_T35TRUN1D.txt@@@"
     ]
   },
@@ skipping 84 matching lines @@
     ],
     "name": "[upload logcat] unzip results for example_instrumentation_suite",
     "stdin": "{\"output\": \"[TMP_BASE]/amp_results_tmp_2/T35TRUN1D/unzipped_results\", \"zip_file\": \"[TMP_BASE]/amp_results_tmp_2/T35TRUN1D/results.zip\"}"
   },
   {
     "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]/amp_results_tmp_2/T35TRUN1D/unzipped_results/appurify_results/logcat.txt",
       "gs://chrome-amp-results/logcats/logcat_example_instrumentation_suite_T35TRUN1D.txt"
     ],
     "name": "gsutil [upload logcat] example_instrumentation_suite",
     "~followup_annotations": [
       "@@@STEP_LINK@logcat@https://storage.cloud.google.com/chrome-amp-results/logcats/logcat_example_instrumentation_suite_T35TRUN1D.txt@@@"
     ]
   },
@@ skipping 82 matching lines @@
     ],
     "name": "[upload logcat] unzip results for example_uirobot_suite",
     "stdin": "{\"output\": \"[TMP_BASE]/amp_results_tmp_2/T35TRUN1D/unzipped_results\", \"zip_file\": \"[TMP_BASE]/amp_results_tmp_2/T35TRUN1D/results.zip\"}"
   },
   {
     "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]/amp_results_tmp_2/T35TRUN1D/unzipped_results/appurify_results/logcat.txt",
       "gs://chrome-amp-results/logcats/logcat_example_uirobot_suite_T35TRUN1D.txt"
     ],
     "name": "gsutil [upload logcat] example_uirobot_suite",
     "~followup_annotations": [
       "@@@STEP_LINK@logcat@https://storage.cloud.google.com/chrome-amp-results/logcats/logcat_example_uirobot_suite_T35TRUN1D.txt@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]