add logger. catch exception if no backends are available.

- added a logger like stats.js
- converted call to `util.log()` to use logger `l.log()` (would throw exception otherwise since util was not imported)
- if no backends are available, the app would exit with an error calling `split()` on undefined `statsd_host` returned from `ring.get()`. Instead, catch this and report an error in the logs, but do not exit.