RiemannReporter does not close connection to Riemann server when it's told to stop()

[mallman]

RiemannReporter (https://github.com/aphyr/riemann-java-client/blob/c7ef74cdae1cd53a66395d13fbf1ae0a5a81244e/metrics3-riemann-reporter/src/main/java/com/codahale/metrics/riemann/RiemannReporter.java) needs to override the stop() method of ScheduledReporter to close the Riemann server connection it holds. Otherwise, it leaves a dangling connection and non-daemon thread which prevents application termination.