Code review comment for lp:~rvb/maas/no-dhcp-write-of-unvalid-config

> What happens when the last interface is removed from a cluster, leaving it
> with no interfaces?

I see that this code has been recently modified by https://code.launchpad.net/~julian-edwards/maas/stop-dhcp-server-bug-1283114/+merge/207870. I think the behavior introduced by this branch is wrong: it created an invalid config file when the number of managed interfaces was down to zero.

I think the only sensible thing to do is to stop the DHCP server when the number of managed interfaces is zero. I see we already have a task for that so it's just a matter of hooking it up into configure_dhcp(). What do you think?