Fix balance-masters functionality in the new LeadershipService based device mastership store

Change-Id: I9f64d514cee7d5a5383fd4c2fa30a8616c97785c
diff --git a/core/store/trivial/src/main/java/org/onosproject/store/trivial/impl/SimpleLeadershipManager.java b/core/store/trivial/src/main/java/org/onosproject/store/trivial/impl/SimpleLeadershipManager.java
index 5f7bb92..d00f616 100644
--- a/core/store/trivial/src/main/java/org/onosproject/store/trivial/impl/SimpleLeadershipManager.java
+++ b/core/store/trivial/src/main/java/org/onosproject/store/trivial/impl/SimpleLeadershipManager.java
@@ -119,4 +119,14 @@
     public List<NodeId> getCandidates(String path) {
         return null;
     }
+
+    @Override
+    public boolean stepdown(String path) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean makeTopCandidate(String path, NodeId nodeId) {
+        throw new UnsupportedOperationException();
+    }
 }