Add sentinels to logs and qlogs (#1205)

* sentinel WIP

* logger is now a cc, not a c

* simpler code doesn't touch loggerd.cc

* oops, double lock. and logreader is nicer

tools/lib/logreader.py

@@ -1,3 +1,4 @@
+#!/usr/bin/env python3
 import os
 import sys
 import json