'When host key verification fails, record the reason for the failure in
order to fire a L{Deferred} with it later.
@param reason: The cause of the host key verification failure.
@type reason: L{Failure}
@return: C{reason}
@rtype: L{Failure}'

def _saveHostKeyFailure(self, reason):

    self._hostKeyFailure = reason
    return reason
