[Fix for Bug 1631]

[Fix for Bug 1631]
- Refactored RaftActorBehavior#handleMessage (and related methods) to return RaftActorBehavior
  instead of RaftActorState.
- Moved behavior switching from RaftActor based on requested state to the implementations of the
  behaviors that should control that switch (Leader/Follower/Candidate) based on the type of
  message received.
- Pull up logger reference for concrete RAFT behaviors to parent for a common LOG reference.
- Updated all logger calls to:
 	- Use substitution instead of String concatenation.
	- Debug logger calls are gated by isDebugEnabled check.
	- Correctly use Akka logging API for stack trace on exception.
	- Avoid toString() calls during logging.
	- Use assigned logger instance (LOG) instead of call to context.getLogger()

Change-Id: I376e21734a0540aae714fe9ef1562d74e73e558b
Signed-off-by: mark.mozolewski <mark.mozolewski@hp.com>