Add descriptive message for MessagingExceptions.

We can print this message in EventuallyConsistentMapImpl rather than printing
a stack trace which doesn't add any value because the exception always comes
from the same place.

Change-Id: Ia233e7ae8605b2b59ffd4ef834209fdaa86e9376
diff --git a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/EventuallyConsistentMapImpl.java b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/EventuallyConsistentMapImpl.java
index ffbb0c5..bba165f 100644
--- a/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/EventuallyConsistentMapImpl.java
+++ b/core/store/primitives/src/main/java/org/onosproject/store/primitives/impl/EventuallyConsistentMapImpl.java
@@ -588,7 +588,8 @@
                 peer)
                 .whenComplete((result, error) -> {
                     if (error != null) {
-                        log.debug("Failed to send anti-entropy advertisement to {}", peer, error);
+                        log.debug("Failed to send anti-entropy advertisement to {}: {}",
+                                peer, error.getMessage());
                     } else if (result == AntiEntropyResponse.PROCESSED) {
                         antiEntropyTimes.put(peer, adCreationTime);
                     }
@@ -603,7 +604,8 @@
                 peer)
                 .whenComplete((result, error) -> {
                     if (error != null) {
-                        log.debug("Failed to send update request to {}", peer, error);
+                        log.debug("Failed to send update request to {}: {}",
+                                peer, error.getMessage());
                     }
                 });
     }