Checks if the given id is used in the host by some actor.

        :param str. aid: identifier of the actor to check.
        :return: True if the id is used within the host.

def has_actor(self, aid):
        '''
        Checks if the given id is used in the host by some actor.

        :param str. aid: identifier of the actor to check.
        :return: True if the id is used within the host.
        '''
        url = '%s://%s/%s' % (self.transport, self.host_url.netloc, aid)
        return url in self.actors.keys()