Log failure when cleaning shard follow task (#51971)

When clenaing a shard follow task after an index has been deleted, an
exception can occur submitting the complete persistent task
action. However, this exception message is not logged. This commit
addresses this by including the exception that led to the failure in the
log message.

Author: jasontedor

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/ShardFollowTaskCleaner.java

@@ -8,6 +8,7 @@
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.message.ParameterizedMessage;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.client.Client;
 import org.elasticsearch.cluster.ClusterChangedEvent;
@@ -63,9 +64,9 @@ public void clusterChanged(final ClusterChangedEvent event) {
                 // the index exists, do not clean this persistent task
                 continue;
             }
-            IndexNotFoundException e = new IndexNotFoundException(followerIndex);
+            IndexNotFoundException infe = new IndexNotFoundException(followerIndex);
             CompletionPersistentTaskAction.Request request =
-                new CompletionPersistentTaskAction.Request(persistentTask.getId(), persistentTask.getAllocationId(), e);
+                new CompletionPersistentTaskAction.Request(persistentTask.getId(), persistentTask.getAllocationId(), infe);
             threadPool.generic().submit(() -> {
                 client.execute(CompletionPersistentTaskAction.INSTANCE, request, new ActionListener<PersistentTaskResponse>() {
 
@@ -76,7 +77,7 @@ public void onResponse(PersistentTaskResponse persistentTaskResponse) {
 
                     @Override
                     public void onFailure(Exception e) {
-                        logger.warn("failed to clean up task [{}]", persistentTask.getId());
+                        logger.warn(new ParameterizedMessage("failed to clean up task [{}]", persistentTask.getId()), e);
                     }
                 });
             });