ad more info when rejecting execution

src/main/java/org/elasticsearch/common/util/concurrent/EsAbortPolicy.java

@@ -30,6 +30,6 @@ public class EsAbortPolicy implements RejectedExecutionHandler {
 
     @Override
     public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
-        throw new EsRejectedExecutionException();
+        throw new EsRejectedExecutionException("rejected execution of [" + r.getClass().getName() + "]");
     }
 }

src/main/java/org/elasticsearch/common/util/concurrent/EsRejectedExecutionException.java

@@ -26,6 +26,10 @@ import org.elasticsearch.rest.RestStatus;
  */
 public class EsRejectedExecutionException extends ElasticSearchException {
 
+    public EsRejectedExecutionException(String message) {
+        super(message);
+    }
+
     public EsRejectedExecutionException() {
         super(null);
     }