Move update_engine to late_start init class.

This guarantees that /data is decrypted and mounted by the time the
daemon starts.

Bug: 23186405
Change-Id: Iabd444ac786e668a79cedf10c294d3daa336dd44
diff --git a/update_engine.rc b/update_engine.rc
index 1b48da4..3d673a7 100644
--- a/update_engine.rc
+++ b/update_engine.rc
@@ -2,6 +2,6 @@
     mkdir /data/misc/update_engine 0700 system system
 
 service update_engine /system/bin/update_engine --logtostderr --foreground
-    class main
+    class late_start
     user system
     group system dbus inet