recovery: Blank screen during shutdown and reboot

Some hardware doesn't like having the panel on and still
active during power cycles, so just turn it off.

(based on Ied1f0802f5a2d45980ee33abf2456a291ba64beb)

Change-Id: Ied6bbc3a32fd1c7cf6ea3ec1b2bee298520651c3
diff --git a/recovery_ui/ui.cpp b/recovery_ui/ui.cpp
index aed6f49..aced5b0 100644
--- a/recovery_ui/ui.cpp
+++ b/recovery_ui/ui.cpp
@@ -223,6 +223,12 @@
   return true;
 }
 
+void RecoveryUI::Stop() {
+  if (!android::base::WriteStringToFile("0", BRIGHTNESS_FILE)) {
+    PLOG(WARNING) << "Failed to write brightness file";
+  }
+}
+
 void RecoveryUI::OnTouchEvent() {
   Point delta = touch_pos_ - touch_start_;
   enum SwipeDirection { UP, DOWN, RIGHT, LEFT } direction;