Avoid to use environment.

scripts/slave/recipes/chromium_trybot.expected/webkit_tests_unexpected_error.json

 [
   {
     "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",
       "[BUILDER_CACHE]/linux_layout",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 359 matching lines @@
       "--gsutil-py-path",
       "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "--ninja-path",
       "RECIPE_PACKAGE_REPO[depot_tools]/ninja",
       "--target",
       "Release",
       "--src-dir",
       "[BUILDER_CACHE]/linux_layout/src",
       "--goma-cache-dir",
       "[GOMA_CACHE]",
+      "--buildbot-buildername",
+      "linux_precise_blink_rel",
+      "--buildbot-mastername",
+      "tryserver.blink",
+      "--buildbot-slavename",
+      "TestSlavename",
       "--goma-deps-cache-dir",
       "[GOMA_DEPS_CACHE]",
       "--compiler",
       "goma",
       "--goma-jsonstatus",
       "/path/to/tmp/json",
       "--goma-service-account-json-file",
       "/creds/service_accounts/service-account-goma-client.json",
       "--goma-dir",
       "[CACHE]/cipd/goma",
@@ skipping 113 matching lines @@
       "@@@SET_BUILD_PROPERTY@failure_hash@\"a860d9d78c0340ef1c42d9fa74626fe7b110eeb0\"@@@"
     ]
   },
   {
     "name": "$result",
     "reason": "1 out of 1 aggregated steps failed. Failures: Step('webkit_tests') failed with return_code 1",
     "recipe_result": null,
     "status_code": 1
   }
 ]