Called when ssh transport requests us to verify a given host key.
        Return a deferred that callback if we accept the key or errback if we
        decide to reject it.

def _verifyHostKey(self, hostKey, fingerprint):
        """Called when ssh transport requests us to verify a given host key.
        Return a deferred that callback if we accept the key or errback if we
        decide to reject it.
        """
        if fingerprint in self.knownHosts:
            return defer.succeed(True)
        return defer.fail(UnknownHostKey(hostKey, fingerprint))