Create a BIP0032-style hierarchical wallet.

        @param: master_secret Create from master secret, otherwise random.

def create_wallet(self, master_secret=b""):
        """Create a BIP0032-style hierarchical wallet.

        @param: master_secret Create from master secret, otherwise random.
        """
        master_secret = deserialize.bytes_str(master_secret)
        bip32node = control.create_wallet(self.testnet,
                                          master_secret=master_secret)
        return bip32node.hwif(as_private=True)