The bdutil script does not handle parameters in order to tag the VM during their creation. Nevertheless you could try to modify the following section of the script:
run_gcutil_cmd \
addinstance \
--machine_type=${GCE_MACHINE_TYPE} \
--service_account=default \
--image=${GCE_IMAGE} \
--network=${GCE_NETWORK} \
--service_account_scopes=${GCE_SERVICE_ACCOUNT_SCOPES} \
--persistent_boot_disk \
--external_ip_address=ephemeral \
${optional_disk_arg} ${MASTER_HOSTNAME} &
await_async_jobs 'addinstance'
You would have to use the gcloud command which replaces gcutil and is able to tag the instances as well as using the other parameters (i.e zone, machine type, image, etc). You can refer to https://cloud.google.com/compute/docs/instances#tags.