add support for testing sensor resets

Change-Id: I469609445904d8eca1d11ee756998ba8801465ea
diff --git a/aos/common/controls/control_loop_test.cc b/aos/common/controls/control_loop_test.cc
index 40357b2..fd461b6 100644
--- a/aos/common/controls/control_loop_test.cc
+++ b/aos/common/controls/control_loop_test.cc
@@ -40,7 +40,7 @@
   {
     auto new_state = ::aos::robot_state.MakeMessage();
 
-    new_state->reader_pid = 971;
+    new_state->reader_pid = reader_pid_;
     new_state->outputs_enabled = enabled;
     new_state->browned_out = false;