Send NexusStoppedEvent event on test teardown

This allows components like Hc4ProviderImpl to properly showdown when a test ends and such avoid OOM

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
Merge pull request #750 from sonatype/send-nexus-stopped-in-tests

Send NexusStoppedEvent event on test teardown