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/api/src/main/java/org/onosproject/store/cluster/messaging/MessagingException.java b/core/api/src/main/java/org/onosproject/store/cluster/messaging/MessagingException.java
index ce47258..d0b8cbb 100644
--- a/core/api/src/main/java/org/onosproject/store/cluster/messaging/MessagingException.java
+++ b/core/api/src/main/java/org/onosproject/store/cluster/messaging/MessagingException.java
@@ -42,17 +42,26 @@
      * Exception indicating no remote registered remote handler.
      */
     public static class NoRemoteHandler extends MessagingException {
+        public NoRemoteHandler() {
+            super("No remote message handler registered for this message");
+        }
     }
 
     /**
      * Exception indicating handler failure.
      */
     public static class RemoteHandlerFailure extends MessagingException {
+        public RemoteHandlerFailure() {
+            super("Remote handler failed to handle message");
+        }
     }
 
     /**
-     * Exception indicating failure due to invalid message strucuture such as an incorrect preamble.
+     * Exception indicating failure due to invalid message structure such as an incorrect preamble.
      */
-    public static class ProcotolException extends MessagingException {
+    public static class ProtocolException extends MessagingException {
+        public ProtocolException() {
+            super("Failed to process message due to invalid message structure");
+        }
     }
-}
\ No newline at end of file
+}