Add a Quit RPC so that we can conveniently shut down the workers from the driver.
diff --git a/test/cpp/qps/worker.cc b/test/cpp/qps/worker.cc
index a1e73e9..f42cfe3 100644
--- a/test/cpp/qps/worker.cc
+++ b/test/cpp/qps/worker.cc
@@ -56,7 +56,7 @@
 static void RunServer() {
   QpsWorker worker(FLAGS_driver_port, FLAGS_server_port);
 
-  while (!got_sigint) {
+  while (!got_sigint && !worker.Done()) {
     gpr_sleep_until(gpr_time_add(gpr_now(GPR_CLOCK_REALTIME),
                                  gpr_time_from_seconds(5, GPR_TIMESPAN)));
   }