dpdk_telemetry plugin: add plugin for DPDK metrics via DPDK Telemetry library

dpdk_telemetry plugin: add plugin for DPDK metrics via DPDK Telemetry library

This patch introduces a new plugin for collectd, which consumes DPDK metrics
via the dpdk_telemetry library. The collectd plugin here provides an
easy way to use the DPDK telemetry API to query ethernet device metrics.

The collectd plugin retrieves metrics from a DPDK packet forwarding
application by sending a JSON formatted message via a UNIX domain
socket. The DPDK telemetry component will respond with a JSON formatted
reply, delivering the requested metrics. The dpdk_telemetry collectd
plugin parses the JSON data, and publishes the metric values to collectd
for further use.

This plugin has a dependency on the DPDK Telemetry library, as it must be
"in sync" with the DPDK Telemetry implementation.

Change-Id: If3343aae4c5473f0574465fab0395b7672fa2488
Signed-off-by: Emma Kenny <emma.kenny@intel.com>
Signed-off-by: Brian Archbold <brian.archbold@intel.com>
Signed-off-by: Reshma Pattan <reshma.pattan@intel.com>