lp:~jtv/maas/bug-1084507

This branch should be almost enough to solve the problem. But it introduces a celery config import into the tftpd, which as far as I can make out doesn't have any celery imports yet. And that means that whatever starts up the tftpd must tell it to use the cluster celery config, not the default celeryconfig.py. I haven't pinpointed where that should happen yet; it may be a packaging change.