[SPARK-15121] Improve logging of external shuffle handler

## What changes were proposed in this pull request?

Add more informative logging in the external shuffle service to aid in debugging who is connecting to the YARN Nodemanager when the external shuffle service runs under it.

## How was this patch tested?

Ran and saw logs coming out in log file.

Author: Thomas Graves <[email protected]>

Closes #12900 from tgravescs/SPARK-15121.

Author: Thomas Graves

common/network-shuffle/src/main/java/org/apache/spark/network/shuffle/ExternalShuffleBlockHandler.java

@@ -35,6 +35,7 @@
 import org.apache.spark.network.server.StreamManager;
 import org.apache.spark.network.shuffle.ExternalShuffleBlockResolver.AppExecId;
 import org.apache.spark.network.shuffle.protocol.*;
+import org.apache.spark.network.util.NettyUtils;
 import org.apache.spark.network.util.TransportConf;
 
 
@@ -86,7 +87,8 @@ protected void handleMessage(
         blocks.add(blockManager.getBlockData(msg.appId, msg.execId, blockId));
       }
       long streamId = streamManager.registerStream(client.getClientId(), blocks.iterator());
-      logger.trace("Registered streamId {} with {} buffers", streamId, msg.blockIds.length);
+      logger.trace("Registered streamId {} with {} buffers for client {} from host {}", streamId, 
+        msg.blockIds.length, client.getClientId(), NettyUtils.getRemoteAddress(client.getChannel()));
       callback.onSuccess(new StreamHandle(streamId, msg.blockIds.length).toByteBuffer());
 
     } else if (msgObj instanceof RegisterExecutor) {