Replacing <classifier>tests</classifier> with <type>test-jar</type>
Merge pull request #453 from whikloj/topic-74718106

Replacing <classifier>tests</classifier> with <type>test-jar</type>
Change RegistryService to singleton, and add unit test

- Remove static from declaration of RegistryService (metrics)

Resolves: https://www.pivotaltracker.com/story/show/77113576
Minor code cleanup
Upgrading Metrics libraries to latest stable offerings from Dropwizard