ClusterMessagingProtocolClient: add log

Change-Id: Ic85fc765cc4140af0d69fd4ccccd091634b8deca
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/ClusterMessagingProtocolClient.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/ClusterMessagingProtocolClient.java
index 976fbcf..be0da20 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/ClusterMessagingProtocolClient.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/ClusterMessagingProtocolClient.java
@@ -145,6 +145,7 @@
                     future.completeExceptionally(e);
                 }
             } catch (Exception e) {
+                log.warn("RPCTask for {} terribly failed.", request, e);
                 future.completeExceptionally(e);
             }
         }