Avoid to use environment.

scripts/slave/recipes/webrtc/standalone.expected/client_webrtc_mac64_debug.json

 [
   {
     "cmd": [
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/ios/host_info.py",
       "--json-file",
       "/path/to/tmp/json"
     ],
     "name": "host and tools info",
     "~followup_annotations": [
       "@@@STEP_TEXT@<br />OS X 1.2.3, Xcode 6.7.8 (5D342509a)@@@",
@@ skipping 239 matching lines @@
       "--gsutil-py-path",
       "RECIPE_PACKAGE_REPO[depot_tools]/gsutil.py",
       "--ninja-path",
       "RECIPE_PACKAGE_REPO[depot_tools]/ninja",
       "--target",
       "Debug",
       "--src-dir",
       "[BUILDER_CACHE]/Mac64_Debug/src",
       "--goma-cache-dir",
       "[GOMA_CACHE]",
+      "--buildbot-buildername",
+      "Mac64 Debug",
+      "--buildbot-mastername",
+      "client.webrtc",
+      "--buildbot-slavename",
+      "slavename",
       "--goma-deps-cache-dir",
       "[GOMA_DEPS_CACHE]",
       "--compiler",
       "goma-clang",
       "--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 409 matching lines @@
     ],
     "cwd": "[BUILDER_CACHE]/Mac64_Debug",
     "name": "webrtc_nonparallel_tests"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]