Bug fixes for ONOS-3509

- Forwarding behavior added to {Device,Link}Store by ONOS-490
  cauesed false update information sent from ONOS node, which has been detached from the cluster,
  to be accepted by rest of the cluster after the detached node has rejoined cluster.

- Fix for periodic mastership check was left out
  when MastershipService#requestRoleFor(..) return value was changed to Future.

- Fix for triggerProbe() related messages getting dropped,
  right after STANDBY -> MASTER role change.

- Local state (connectedDevices) was preventing
  vertical (Core -> switch) Mastership state synchronization.

- Various debug log, comment added during investigation.

Change-Id: I777beadf04db8a879830a07bfdc7ab0e2279f190
diff --git a/core/api/src/main/java/org/onosproject/cluster/LeadershipEvent.java b/core/api/src/main/java/org/onosproject/cluster/LeadershipEvent.java
index faf6dd4..d1fe670 100644
--- a/core/api/src/main/java/org/onosproject/cluster/LeadershipEvent.java
+++ b/core/api/src/main/java/org/onosproject/cluster/LeadershipEvent.java
@@ -31,20 +31,23 @@
      */
     public enum Type {
         /**
-         * Signifies that the leader has been elected. The event subject is the
-         * new leader.
+         * Signifies that the leader has been elected.
+         * The event subject is the new leader.
+         * This event does not guarantee accurate candidate information.
          */
         LEADER_ELECTED,
 
         /**
-         * Signifies that the leader has been re-elected. The event subject is the
-         * leader.
+         * Signifies that the leader has been re-elected.
+         * The event subject is the leader.
+         * This event does not guarantee accurate candidate information.
          */
         LEADER_REELECTED,
 
         /**
-         * Signifies that the leader has been booted and lost leadership. The
-         * event subject is the former leader.
+         * Signifies that the leader has been booted and lost leadership.
+         * The event subject is the former leader.
+         * This event does not guarantee accurate candidate information.
          */
         LEADER_BOOTED,