Streamline upstart scripts in os-svc-daemon

Best practice is to use start-stop-daemon rather than sudo, as sudo will
apply user-centric pam limits and create a wtmp entry. Also there is no
need for a script stanza, as we are only execing one command.

Change-Id: I0c2f12536b56d90fd43ab40e74424350efcc0b61

elements/os-svc-install/bin/os-svc-daemon

@@ -19,9 +19,7 @@ end script
 
 respawn
 
-script
-  exec sudo -u $user /opt/stack/venvs/$user/bin/$cmd $args
-end script
+exec start-stop-daemon --start -c $user --exec /opt/stack/venvs/$user/bin/$cmd $args
 EOF
 }