Add the job to the waiting list, at the end (it's a fifo list). If
        `prepend` is True, add it at the beginning of the list.

def enqueue_job(self, job, prepend=False):
        """
        Add the job to the waiting list, at the end (it's a fifo list). If
        `prepend` is True, add it at the beginning of the list.
        """
        push_method = getattr(self.waiting, 'lpush' if prepend else 'rpush')
        push_method(job.ident)