Add leader unit test for non-voting consensus

Added a test case to LeaderTest to verify a non-voting follower
does not influence replication consensus.

Also I saw intermitent test failures (in jenkins as well during first
verify build) due to a message going to dead letters shortly after
actor creation (also reported in Bug 4223). Specifically it was occurring
when the leader sent the initial AppendEntries heartbeat to a follower. This
seems like a timing issue/bug in akka when using an ActorSelection. I
added code in the TestActorFactory to use an actorSelection and call
resolveOne in a retry loop. This seems to alleviate the issue as I ran
LeaderTest over 1000 times successfully.

Change-Id: I65cb87f419c280befe2d82300a981bd8e6f88742
Signed-off-by: Tom Pantelis <tpanteli@brocade.com>