use lumberjack for log rolling

This is very similar to the last PR, except I didn't change out the upstart config stuff... since the output redirect doesn't hurt anything, and we need the rest of the code to properly set permissions and owner on the logfile.
The main thing that makes it better is that it pulls the magic consts to a clustered definition, rather than just being somewhere inside the code. That makes it easier to spot them when you need them. I wouldn't put the consts inside the function, but at the top of the file.