Convert control loop tests over to simulated event loop

This makes it so that we properly only use ShmEventLoop for running in
realtime on a robot.  Very nice.

Change-Id: I46b770b336f59e08cfaf28511b3bd5689f72fff1
diff --git a/frc971/control_loops/drivetrain/hybrid_ekf.h b/frc971/control_loops/drivetrain/hybrid_ekf.h
index 68f67f6..16b0b61 100644
--- a/frc971/control_loops/drivetrain/hybrid_ekf.h
+++ b/frc971/control_loops/drivetrain/hybrid_ekf.h
@@ -488,6 +488,9 @@
   // tuning things. I haven't yet tried messing with these values again.
   encoder_noise_ = 0.5 * R_kf_drivetrain(0, 0);
   gyro_noise_ = 0.1 * R_kf_drivetrain(2, 2);
+
+  X_hat_.setZero();
+  P_.setZero();
 }
 
 }  // namespace drivetrain