gce: extend CLOBBER_CONFIG to support known_tokens.csv

cluster/gce/gci/configure-helper.sh

@@ -359,7 +359,11 @@ function create-master-auth {
     fi
     append_or_replace_prefixed_line "${basic_auth_csv}" "${KUBE_PASSWORD},${KUBE_USER},"      "admin,system:masters"
   fi
+
   local -r known_tokens_csv="${auth_dir}/known_tokens.csv"
+  if [[ -e "${known_tokens_csv}" && "${METADATA_CLOBBERS_CONFIG:-false}" == "true" ]]; then
+    rm "${known_tokens_csv}"
+  fi
   if [[ -n "${KUBE_BEARER_TOKEN:-}" ]]; then
     append_or_replace_prefixed_line "${known_tokens_csv}" "${KUBE_BEARER_TOKEN},"             "admin,admin,system:masters"
   fi