Clustering : Refactor RaftActor to remove the need for RaftState

RaftActor maintains a state machine where the state is represented by the RaftActorBehavior. It also maintains an enumeration called RaftState which basically nothing but the "friendly" name of the RaftActorBehavior which can be passed around.

The RaftActorBehavior is mutable so if we do need to pass it around even to sub-classes we need to do it carefully hence for now this refactoring is deferred till after Helium.