Add Riemann metrics reporter for codahale metrics >= 3
Add unit tests for metrics 3 RiemannReporter

Also updated the Riemann client wrapper class to be more testable.
Basically took the GraphiteReporter's unit tests and updated them to
work with Riemann.

Test custom separators in the RiemannReporter
Add old-style vmmetric metricset
Merge pull request #35 from dlobue/codahale_metrics_3_reporter

Codahale metrics 3 reporter