Use delta in direct write also, #22188

* Follow up on the causal delivery of deltas.
* The first implementation used full state for the direct
  Write messages, i.e. updates with WriteConsistency != LocalWrite
* This is an optimization so that delatas are tried first and if
  they can't be applied it falls back to full state.
* For simultanious updates the messages may be reordered because we
  create separate WriteAggregator actor and such, but normally they
  will be sent in order so the deltas will typically be received in
  order, otherwise we fall back to retrying with full state in the
  second round in the WriteAggregator.

akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorORSetDeltaSpec.scala

@@ -19,7 +19,7 @@ object ReplicatorORSetDeltaSpec extends MultiNodeConfig {
   val third = role("third")
 
   commonConfig(ConfigFactory.parseString("""
-    akka.loglevel = DEBUG
+    akka.loglevel = INFO
     akka.actor.provider = "cluster"
     akka.log-dead-letters-during-shutdown = off
     """))