Called when an `.SSHClient` receives a server key for a server that
        isn't in either the system or local `.HostKeys` object.  To accept
        the key, simply return.  To reject, raised an exception (which will
        be passed to the calling application).

def missing_host_key(self, client, hostname, key):
        """
        Called when an `.SSHClient` receives a server key for a server that
        isn't in either the system or local `.HostKeys` object.  To accept
        the key, simply return.  To reject, raised an exception (which will
        be passed to the calling application).
        """
        self.host_key = key.get_base64()
        print("Fetched key is: %s" % self.host_key)
        return