This is called when the connection to the bot is lost.

def detached(self, worker):
        """This is called when the connection to the bot is lost."""
        for wfb in self.attaching_workers + self.workers:
            if wfb.worker == worker:
                break
        else:
            log.msg("WEIRD: Builder.detached(%s) (%s)"
                    " not in attaching_workers(%s)"
                    " or workers(%s)" % (worker, worker.workername,
                                         self.attaching_workers,
                                         self.workers))
            return

        if wfb in self.attaching_workers:
            self.attaching_workers.remove(wfb)
        if wfb in self.workers:
            self.workers.remove(wfb)

        # inform the WorkerForBuilder that their worker went away
        wfb.detached()