Require a couple cycles of being disabled.

The arm goes back to the DISABLED state (and therefore the GOTO_PATH
state afterwords) if it gets disabled due to brownouts.  Require a
couple cycles of being disabled before we switch states.  The arm can't
move fast enough to be a problem for short brownouts.

Change-Id: I9d579f2912f3555837dbfab3d30782a289158cd1
diff --git a/y2018/control_loops/superstructure/arm/arm.h b/y2018/control_loops/superstructure/arm/arm.h
index d3dd2df..a9b3590 100644
--- a/y2018/control_loops/superstructure/arm/arm.h
+++ b/y2018/control_loops/superstructure/arm/arm.h
@@ -110,6 +110,7 @@
   bool close_enough_for_full_power_ = false;
 
   int32_t climb_count_ = 0;
+  int32_t brownout_count_ = 0;
 
   EKF arm_ekf_;
   TrajectoryFollower follower_;