cros mod_image_for_factory: don't enable update engine for factory test images (ToT to factory)

To get best factory test image performance, we should disable update engine.

Cherry-picked from: http://codereview.chromium.org/6759023/

TBR=nsanders
BUG=chromium-os:13613
TEST=image_to_usb --factory --to=FACTORY
     then verified /etc/init/update-engine.conf is disabled.

Change-Id: Ifb7b6c821f434ee68625ffea0eb7907c38d77315

R=nsanders@chromium.org

Review URL: http://codereview.chromium.org/6765025
diff --git a/mod_for_factory_scripts/200patchInitScript b/mod_for_factory_scripts/200patchInitScript
index 422d8af..7f6bc0c 100755
--- a/mod_for_factory_scripts/200patchInitScript
+++ b/mod_for_factory_scripts/200patchInitScript
@@ -73,6 +73,17 @@
 end script
 EOF
 
+if [ -r "${ROOT_FS_DIR}/etc/init/update-engine.conf" ]; then
+  patch -d "${ROOT_FS_DIR}" -Np1 <<EOF
+diff -Na -U 0 old/etc/init/update-engine.conf new/etc/init/
+--- old/etc/init/update-engine.conf	2010-08-05 16:32:55.000000000 -0700
++++ new/etc/init/update-engine.conf	2010-08-05 16:32:45.000000000 -0700
+@@ -8 +8 @@
+-start on starting system-services and started dbus
++start on never
+EOF
+fi
+
 if [ -r "${ROOT_FS_DIR}/etc/init/chrontel.conf" ]; then
   patch -d "${ROOT_FS_DIR}" -Np1 <<EOF
 diff -Nau old/etc/init/chrontel.conf new/etc/init/