Complete future after Leadership withdraw is done

Change-Id: I905a78c3f80e10793506ac92783d502798ae0390

@@ -289,6 +289,7 @@ public class DistributedLeadershipManager implements LeadershipService {
                                    (topic, candidates) -> candidates.stream()
                                                                     .filter(nodeId -> !localNodeId.equals(nodeId))
                                                                     .collect(Collectors.toList()));
+            future.complete(null);
         } catch (Exception e) {
             log.debug("Failed to verify (and clear) any lock this node might be holding for {}", path, e);
             retryWithdraw(path, future);