log uncaught Exception

- Use execute instead of submit so that uncaught Exception will
  be dealt and logged by ExecutorService's handler.
- Use component's own logger

Change-Id: I761264aea00748980929b5048e111756776dd2f6
diff --git a/core/store/dist/src/main/java/org/onosproject/store/group/impl/DistributedGroupStore.java b/core/store/dist/src/main/java/org/onosproject/store/group/impl/DistributedGroupStore.java
index a28e4ee..a142e5f 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/group/impl/DistributedGroupStore.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/group/impl/DistributedGroupStore.java
@@ -185,7 +185,8 @@
         messageHandlingExecutor = Executors.
                 newFixedThreadPool(MESSAGE_HANDLER_THREAD_POOL_SIZE,
                                    groupedThreads("onos/store/group",
-                                                  "message-handlers"));
+                                                  "message-handlers",
+                                                  log));
 
         clusterCommunicator.addSubscriber(GroupStoreMessageSubjects.REMOTE_GROUP_OP_REQUEST,
                                           clusterMsgSerializer::deserialize,