Use GID "wakelock" to control access to kernel wakelock

Bug: 25864142
Change-Id: I7128248d5ec87d21374998e818fb6b69441e4c5b
diff --git a/update_engine.rc b/update_engine.rc
index 69fc7af..499a8f6 100644
--- a/update_engine.rc
+++ b/update_engine.rc
@@ -1,4 +1,4 @@
 service update_engine /system/bin/update_engine --logtostderr --foreground
     class late_start
     user root
-    group root system dbus inet
+    group root system wakelock dbus inet