Disable update_engine by default.

Until SELinux policy is fully fleshed out, we don't want update_engine
failing and polluting the syslog.

Bug: 23186405
Change-Id: I7c9495aff3028f87727f881caa70d2e4a82d5e09
diff --git a/update_engine.rc b/update_engine.rc
index 3d673a7..fe5b224 100644
--- a/update_engine.rc
+++ b/update_engine.rc
@@ -5,3 +5,4 @@
     class late_start
     user system
     group system dbus inet
+    disabled