Improve Executors related logging behavior

- Specify Logger for the Executor
- Use Executor#execute instead of ExecutorService#submit for
  fire and forget type of usage.
   Note: submit() will swallow thrown Exception

Change-Id: I507b841dc3feedf4ad20a746c304518d68fb846a
diff --git a/core/store/dist/src/main/java/org/onosproject/store/statistic/impl/DistributedFlowStatisticStore.java b/core/store/dist/src/main/java/org/onosproject/store/statistic/impl/DistributedFlowStatisticStore.java
index 8e59ef6..c3f907a 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/statistic/impl/DistributedFlowStatisticStore.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/statistic/impl/DistributedFlowStatisticStore.java
@@ -118,7 +118,7 @@
 
         messageHandlingExecutor = Executors.newFixedThreadPool(
                 messageHandlerThreadPoolSize,
-                groupedThreads("onos/store/statistic", "message-handlers"));
+                groupedThreads("onos/store/statistic", "message-handlers", log));
 
         clusterCommunicator.addSubscriber(
                 GET_CURRENT, SERIALIZER::decode, this::getCurrentStatisticInternal, SERIALIZER::encode,
@@ -200,6 +200,7 @@
         previous.computeIfPresent(cp, (c, e) -> { e.remove(rule); return e; });
     }
 
+    @Override
     public synchronized void updateFlowStatistic(FlowEntry rule) {
         ConnectPoint cp = buildConnectPoint(rule);
         if (cp == null) {