Renamed AbstractListenerRegistry to ListenerRegistry (since it is not abstract).
- added checkForNonRegistrant() predicate and augmented unit tests.

Change-Id: I7ecc618f01fdc4cead6f143a1e5e0ddd03268efc
diff --git a/core/store/dist/src/main/java/org/onosproject/store/consistent/impl/DistributedLeadershipManager.java b/core/store/dist/src/main/java/org/onosproject/store/consistent/impl/DistributedLeadershipManager.java
index 69a1a8a..a013737 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/consistent/impl/DistributedLeadershipManager.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/consistent/impl/DistributedLeadershipManager.java
@@ -19,7 +19,7 @@
 import org.onosproject.cluster.LeadershipEventListener;
 import org.onosproject.cluster.LeadershipService;
 import org.onosproject.cluster.NodeId;
-import org.onosproject.event.AbstractListenerRegistry;
+import org.onosproject.event.ListenerRegistry;
 import org.onosproject.event.EventDeliveryService;
 import org.onosproject.store.cluster.messaging.ClusterCommunicationService;
 import org.onosproject.store.cluster.messaging.MessageSubject;
@@ -85,7 +85,7 @@
     private ConsistentMap<String, NodeId> leaderMap;
     private ConsistentMap<String, List<NodeId>> candidateMap;
 
-    private AbstractListenerRegistry<LeadershipEvent, LeadershipEventListener>
+    private ListenerRegistry<LeadershipEvent, LeadershipEventListener>
         listenerRegistry;
     private final Map<String, Leadership> leaderBoard = Maps.newConcurrentMap();
     private final Map<String, Leadership> candidateBoard = Maps.newConcurrentMap();
@@ -135,7 +135,7 @@
         leadershipStatusBroadcaster.scheduleWithFixedDelay(
                 this::sendLeadershipStatus, 0, LEADERSHIP_STATUS_UPDATE_INTERVAL_SEC, TimeUnit.SECONDS);
 
-        listenerRegistry = new AbstractListenerRegistry<>();
+        listenerRegistry = new ListenerRegistry<>();
         eventDispatcher.addSink(LeadershipEvent.class, listenerRegistry);
 
         log.info("Started");