Make a "fake" txid for a vesting transaction.
    Returns a 32-byte hash (double-sha256), hex-encoded

def namedb_vesting_txid(address, token_type, token_amount, block_height):
    """
    Make a "fake" txid for a vesting transaction.
    Returns a 32-byte hash (double-sha256), hex-encoded
    """
    preimage = '{} vesting {} {} at {}'.format(address, token_type, token_amount, block_height)
    return virtualchain.lib.hashing.bin_double_sha256(preimage).encode('hex')