HDFS-13727. Log full stack trace if DiskBalancer exits with an unhandled exception.

Contributed by Gabor Bota.

(cherry picked from commit 64e739e344ac474046d4f4ecf0865dd92be13762)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/DiskBalancerCLI.java

@@ -165,7 +165,9 @@ public class DiskBalancerCLI extends Configured implements Tool {
     try {
       res = ToolRunner.run(shell, argv);
     } catch (Exception ex) {
-      LOG.error(ex.toString());
+      String msg = String.format("Exception thrown while running %s.",
+          DiskBalancerCLI.class.getSimpleName());
+      LOG.error(msg, ex);
       res = 1;
     }
     System.exit(res);