Header normalization metrics

Building on Damiens branch from here: 
https://github.com/dmnjohns/repose/tree/header-normalization-metrics or https://github.com/dmnjohns/repose/commit/eb944b19d54c04f3b6f5558fc7b0ad39aeaa5338

Added configs and code for the jmx test for header normalization filter.
Added the ability to use dynamic ports and apply configs with variable substitution at run-time.