Add wait-for-tron and wait-for-actor scripts

In order for ics_launch to be useful for a full system boot, various actors will need to wait for the tron hub to come up. Wrap that.

And in a few cases (and actually just for convenience), it will be useful to wait until some actor is running before launching something.

Both cases can I think be handled with minor adaptations of oneCmd.py hub actors. That, unfortunately, depends on tron_actorcore, so purity will have to be set aside.