LeadershipService and MastershipService/Store APIs return CompletableFutures so that callers can (optionally) chain together dependent operations

Change-Id: Ia00fcb7d98fbfce897527f67ea9690abf6fe846a
diff --git a/core/api/src/test/java/org/onosproject/cluster/LeadershipServiceAdapter.java b/core/api/src/test/java/org/onosproject/cluster/LeadershipServiceAdapter.java
index abc92f5..e1d421d 100644
--- a/core/api/src/test/java/org/onosproject/cluster/LeadershipServiceAdapter.java
+++ b/core/api/src/test/java/org/onosproject/cluster/LeadershipServiceAdapter.java
@@ -18,6 +18,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.CompletableFuture;
 
 /**
  * Test adapter for leadership service.
@@ -40,13 +41,13 @@
     }
 
     @Override
-    public void runForLeadership(String path) {
-
+    public CompletableFuture<Leadership> runForLeadership(String path) {
+        return null;
     }
 
     @Override
-    public void withdraw(String path) {
-
+    public CompletableFuture<Void> withdraw(String path) {
+        return null;
     }
 
     @Override