message: Fix the spawn strategy flag.
  Looks like it is not called sandboxed anymore:
  ERROR: 'sandboxed' is an invalid value for sandboxed spawn strategy. Valid values are: local, remote, standalone, worker
diff: @@ -279,7 +279,7 @@ build:rbe --flaky_test_attempts=3
  build:rbe --jobs=200
  build:rbe --remote_executor=grpcs://remotebuildexecution.googleapis.com
  build:rbe --remote_timeout=3600
  -build:rbe --spawn_strategy=remote,worker,sandboxed,local
  +build:rbe --spawn_strategy=remote,worker,standalone,local
  test:rbe --test_env=USER=anon
  build:rbe --distinct_host_configuration=false
  