bin/djbdns-logparse.py: move regex handling down a level.

It was a bit awkward to match a line against a regex, and then to have
to immediately pass that match object into a function that knows what
to do with it (to avoid duplicating work). Now the handle_tinydns_log()
and handle_dnscache_log() functions create the match object themselves,
and signal success or failure by returning a boolean.