Send a last reporting on shutdown, followed by zeroes for *_R

src/main/java/alien/io/protocols/Xrootd.java

src/main/java/alien/monitoring/CacheMonitor.java

src/main/java/alien/monitoring/Counter.java

src/main/java/alien/monitoring/DerivedDataProducer.java

src/main/java/alien/monitoring/Measurement.java

src/main/java/alien/monitoring/Monitor.java

src/main/java/alien/monitoring/MonitorFactory.java