upstart: add stop_job() helper

BUG=chromium:616778
TEST=none

Change-Id: I445266921a79f8d3a17204e7681e3725818fd8ae
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/349678
Reviewed-by: Dan Erat <derat@chromium.org>
diff --git a/client/cros/upstart.py b/client/cros/upstart.py
index 2acf763..3752b2d 100644
--- a/client/cros/upstart.py
+++ b/client/cros/upstart.py
@@ -45,3 +45,13 @@
         utils.system_output('restart %s' % service_name)
     else:
         utils.system_output('start %s' % service_name)
+
+def stop_job(service_name):
+   """
+   Stops an upstart job.
+   Fails if the stop command fails.
+
+   @param service_name: name of service
+   """
+
+   utils.system('stop %s' % service_name)