cbuildbot: migrate legacy builders to RBE_CHROMEOS

This will migrate the builders running on tip-of-tree.

BUG=b:162292728
TEST=unit tests pass

Change-Id: I7f2fd300e12cad9b62055da907cacc606ce51b71
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2569106
Tested-by: LaMont Jones <lamontjones@chromium.org>
Reviewed-by: Navil Perez <navil@google.com>
diff --git a/cbuildbot/stages/build_stages.py b/cbuildbot/stages/build_stages.py
index 8326405..9b465cd 100644
--- a/cbuildbot/stages/build_stages.py
+++ b/cbuildbot/stages/build_stages.py
@@ -632,7 +632,7 @@
     # TODO(crbug.com/751010): Revisit to enable DepsCache for non-chrome-pfq
     # bots, too.
     use_goma_deps_cache = self._run.config.name.endswith('chrome-pfq')
-    goma_approach = goma_util.GomaApproach('?prod', 'goma.chromium.org', True)
+    goma_approach = goma_util.GomaApproach('?cros', 'goma.chromium.org', True)
     goma = goma_util.Goma(
         self._run.options.goma_dir,
         self._run.options.goma_client_json,