engine: rename reconciler -> wipReconciler

The current reconciler is a work-in-progress. Make that obvious.
engine: reintroduce dumb scheduler

Add the old offer-to-all scheduler back as "dumbReconciler". This has
been mostly unmodified, with the exception of replacing the partitioning
of machine IDs with a NOP. Jobs are offered to all machines.
engine: switch back to dumb reconciler