Capture launch errors from stageManager

stageManager start needs to detect when an actor does not launch. As it stands it stdout/stderr get written to a log file, but that is it. I think it should pay attention for a few seconds, and usefully complain if the actor process exits within that time.

As an aside, per INSTRM-322 we will switch to rsyslog logging, so stdio should be piped to logger in any case.