Provide mechanism for detecting Cluster singleton failures and cluster sharding start failures

as discussed: https://groups.google.com/forum/?fromgroups=#!topic/akka-user/_PJtBMzKuAk

Sounds good to publish this on the event bus. It's a fatal error that will not repair itself, so one could claim that we should stop the actor system, but that might be too harsh.

so some failure event should be published when shard coordinator fails to start similar for cluster singleton - when it is stuck, also event can be published

that would allow app monitoring logic to catch failure situation and act upon it