Add instance-specific ProcessName to Hadoop2 metrics

Current Hadoop2 metrics from the tablet servers are not labelled by instance when multiple instances are run on the same host.

By adding a ProcessName tag (Master, TaletServer-1, TabletServer-2, GarbageCollector, etc) to the MetricsRegistry, this tag will be included on all metrics prodeced and allow the Metrics2 sinks to use this information to deconflict these metrics.

The relevant service and instance information can be found in the system properties:
-Dapp and -Daccumulo.service.instance written by the accumulo script.