Register graceful shutdown for list groups command

Change-Id: Ie9d336a9bc278b21026b7094387d5b9d40a053e8

java/com/google/gerrit/sshd/commands/ListGroupsCommand.java

@@ -52,6 +52,7 @@ public class ListGroupsCommand extends SshCommand {
 
   @Override
   public void run() throws Exception {
+    enableGracefulStop();
     if (listGroups.getUser() != null && !listGroups.getProjects().isEmpty()) {
       throw die("--user and --project options are not compatible.");
     }