[AETHER-432][VOL-3263] Revisit meters subsystem to be fully distributed.

- Events are now propagated across the cluster.
- REF_COUNT_ZERO is now generated after the first stats interval.
- SB ops are offloaded to the installers.
- Installers use predictable executors.
- Deprecated MeterData API that exposes origin node and removed unused code.
- Comments are added to parts of the code that are obscure.
- MeterManager and DistributedMeterStore unit tests are improved.
- Fix an issue in TestConsistentMap.

Change-Id: I0329f903e5fdc421f29ee33f8f8133f18c794d8f
diff --git a/core/api/src/test/java/org/onosproject/store/service/TestConsistentMap.java b/core/api/src/test/java/org/onosproject/store/service/TestConsistentMap.java
index aa08c8d..84d1734 100644
--- a/core/api/src/test/java/org/onosproject/store/service/TestConsistentMap.java
+++ b/core/api/src/test/java/org/onosproject/store/service/TestConsistentMap.java
@@ -28,6 +28,7 @@
 import java.util.function.Function;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import org.onosproject.store.primitives.ConsistentMapBackedJavaMap;
 
@@ -278,6 +279,11 @@
     }
 
     @Override
+    public Stream<Map.Entry<K, Versioned<V>>> stream() {
+        return map.entrySet().stream();
+    }
+
+    @Override
     public void addListener(MapEventListener<K, V> listener) {
         listeners.add(listener);
     }