def _holdout(ruleset):
    return ruleset
Build a map of <tier> => <target_replicas> accounting for device
dataset/ETHPy150Open anzev/hedwig/hedwig/stats/adjustment.py/_holdout--crossover with--dataset/ETHPy150Open openstack/swift/swift/common/ring/builder.py/RingBuilder._build_target_replicas_by_tier