Make a "fake" txid for a genesis block entry.
    Returns a 32-byte hash (double-sha256), hex-encoded

def namedb_genesis_txid(address, metadata):
    """
    Make a "fake" txid for a genesis block entry.
    Returns a 32-byte hash (double-sha256), hex-encoded
    """
    preimage = '{} genesis {}'.format(address, metadata)
    return virtualchain.lib.hashing.bin_double_sha256(preimage).encode('hex')