Every reporter implements Reporter interface to indicate that is a Reporter
Merge pull request #480 from druminski/reporterInterface

Every reporter implements Reporter marker interface
Delete ReporterTest.java
metrics-jetty8: Avoid NPE if InstrumentedQueuedThreadPool gauges are read too early
Merge pull request #537 from slovdahl/master

metrics-jetty8: Avoid NPE if InstrumentedQueuedThreadPool gauges are read too early