introduce --stopped for spawner

[Karsten1987]

as per title, the spawner.py script gets an additional --stopped argument to only load & configure the controller, however not starting it.

[destogl]

Thanks, you are clearing my todo list :)

[destogl]

One more idea: to be closer to the ROS1 wording, should be also have am option "--load-only" for this functionality?

[Karsten1987]

I was thinking to replicate what we had in ros2 control load in which we add a --set-state command. But I actually believe the ROS1 wording is --stopped.
From here: http://wiki.ros.org/controller_manager#spawner

$ rosrun controller_manager spawner [--stopped] <name1> <name2> ...