Dual-homing probing improvements

(1) Active probing mechanism in the following two scenarios
    (1-1) Probe all ports on the pair device within the same vlan (excluding the pair port) when the 1st location of a host is learnt
    (1-2) Probe again when a device/port goes down and comes up again
    * Introduce HostLocationProvingService
        - DISCOVER mode: discover potential new locations
        - VERIFY mode: verify old locations
    * Can be enabled/disabled via component config
    * Improve HostHandlerTest to test the probing behavior

(2) Fix an issue that redirection flow doesn't get installed after device re-connects

(3) Temporarily fix a race condition in HostHandler by adding a little bit delay

Change-Id: I33d3fe94a6ca491a88b8e06f65bef11447ead0bf
diff --git a/core/api/src/main/java/org/onosproject/net/host/HostStore.java b/core/api/src/main/java/org/onosproject/net/host/HostStore.java
index 6e98d95..96d3c31 100644
--- a/core/api/src/main/java/org/onosproject/net/host/HostStore.java
+++ b/core/api/src/main/java/org/onosproject/net/host/HostStore.java
@@ -23,6 +23,7 @@
 import org.onosproject.net.Host;
 import org.onosproject.net.HostId;
 import org.onosproject.net.HostLocation;
+import org.onosproject.net.host.HostLocationProbingService.ProbeMode;
 import org.onosproject.net.provider.ProviderId;
 import org.onosproject.store.Store;
 
@@ -65,6 +66,14 @@
     HostEvent removeIp(HostId hostId, IpAddress ipAddress);
 
     /**
+     * Append the specified location to the host entry.
+     *
+     * @param hostId host identification
+     * @param location location to be added
+     */
+    void appendLocation(HostId hostId, HostLocation location);
+
+    /**
      * Removes the specified location from the host entry.
      *
      * @param hostId host identification
@@ -139,10 +148,11 @@
      * retrieves the unique MAC address for the probe.
      *
      * @param hostId ID of the host
-     * @param hostLocation the host location that is under verification
+     * @param connectPoint the connect point that is under verification
+     * @param probeMode probe mode
      * @return probeMac, the source MAC address ONOS uses to probe the host
      */
-    default MacAddress addPendingHostLocation(HostId hostId, HostLocation hostLocation) {
+    default MacAddress addPendingHostLocation(HostId hostId, ConnectPoint connectPoint, ProbeMode probeMode) {
         return MacAddress.NONE;
     }