Depends on [SPARK-5413](https://issues.apache.org/jira/browse/SPARK-5413) / #4209, included here, will rebase once the latter's merged.

Author: Ryan Williams <ryan.blake.williams@gmail.com>

Closes #4218 from ryan-williams/udp and squashes the following commits:

ebae393 [Ryan Williams] Add support for sending Graphite metrics via UDP
cb58262 [Ryan Williams] bump metrics dependency to v3.1.0