crosutils: fixing factory upstart script to allow stopping factory test ui.

Developers may want to run their own factory test UI after finishing the
Google official one, so the "factory" test should be stoppable.

BUG=chrome-os-partner:2456
TEST=build a factory image, install and start factory testing UI,
     then switch to VT2, login and type: "initctl stop factory"
     the screen should switch to a virtual terminal (VT2) without
     hanging / reboot.

Change-Id: I6a9d1c951d48d448f5c83c5f645ea531e8fd1499

Review URL: http://codereview.chromium.org/6567004

mod_for_factory_scripts/200patchInitScript

@@ -48,6 +48,15 @@ else
   ./bin/autotest -t factory -c control >>/var/log/factory.log 2>&1
 fi
 end script
+
+pre-stop script
+  pkill python
+  pkill X
+end script
+
+post-stop script
+  chvt 2
+end script
 EOF
 
 cat >"${ROOT_FS_DIR}/etc/init/factorylog.conf" <<EOF