Catch DNS errors from UDP socket

If repeater is used with hostnames rather than IPs
a DNS resolution error crashes statsd server.
If you have a chain of statsd servers configured
to repeat data down the line this has the potential
to bring down the entire chain.

Attaching an error handler stops dgram socket from
throwing an exception and instead logs to console
Update backends/repeater.js
Use Logger for repeater and don't scream if debug is off
Merge pull request #244 from yarekt/master

Catch DNS errors from UDP socket in Repeater backend