'Update replication_status in model_update if it has changed.'

@staticmethod
def _set_replication_status(diff, model_update):

    if ((not diff) or model_update.get('replication_status')):
        return
    diff_specs = diff.get('extra_specs', {})
    replication_diff = diff_specs.get('replication_enabled')
    if replication_diff:
        is_replicated = vol_utils.is_replicated_str(replication_diff[1])
        if is_replicated:
            replication_status = fields.ReplicationStatus.ENABLED
        else:
            replication_status = fields.ReplicationStatus.DISABLED
        model_update['replication_status'] = replication_status
