Subprocess

Let me start with a story. I wanted to just add hook so I could get in some common way an output from child processes so I could send them to supervisor (you know because of reporting and such). But that was such an idealistic idea. I had to take apart the whole tractor.

So here it's. Complete new and I hope nicer implementation for running scripts and hooks in updater in some common way. Plus few other things that were appended on the way there.

This implements #223 (closed)