Fix cluster 0.11 api changes mostly introduced during round-robin refactoring

A side-effect of the round robin feature and the general code clean-up Ben did, were changes to the API, particularly to the worker exit criteria (meaning of suicide and disconnect).

It didn't look to me like these changes were intentional (they weren't documented or discussed, AFAICT), so I propose these small changes to make the cluster API in v0.11 be backwards compatible to v0.10.

/cc @bnoorduis