LeadershipStore updates:
 - Now tracking leader and candidates for a topic using a single map.
 - Using term numbers that are incremented by one every time a new leader is elected.
 - Introduced a separate LeadershipStore to conform to the  manager-store pattern

Change-Id: I1d03a6c5e8ff0e68ef0c1e3a6c2d425c4856e470
diff --git a/core/api/src/main/java/org/onosproject/cluster/LeadershipAdminService.java b/core/api/src/main/java/org/onosproject/cluster/LeadershipAdminService.java
new file mode 100644
index 0000000..c58ca71
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/cluster/LeadershipAdminService.java
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2016 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.cluster;
+
+/**
+ * Interface for administratively manipulating leadership assignments.
+ */
+public interface LeadershipAdminService {
+
+    /**
+     * Attempts to assign leadership for a topic to a specified node.
+     * @param topic leadership topic
+     * @param nodeId identifier of the node to be made leader
+     * @return true is the transfer was successfully executed. This method returns {@code false}
+     * if {@code nodeId} is not one of the candidates for for the topic.
+     */
+    boolean transferLeadership(String topic, NodeId nodeId);
+
+    /**
+     * Make a node to be the next leader by promoting it to top of candidate list.
+     * @param topic leadership topic
+     * @param nodeId identifier of node to be next leader
+     * @return {@code true} if nodeId is now the top candidate. This method returns {@code false}
+     * if {@code nodeId} is not one of the candidates for for the topic.
+     */
+    boolean promoteToTopOfCandidateList(String topic, NodeId nodeId);
+
+    /**
+     * Removes all active leadership registrations for a given node.
+     * <p>
+     * This method will also evict the node from leaderships that it currently owns.
+     * @param nodeId node identifier
+     */
+    void unregister(NodeId nodeId);
+}