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/apps/segmentrouting/src/test/java/org/onosproject/segmentrouting/MockInterfaceService.java b/apps/segmentrouting/src/test/java/org/onosproject/segmentrouting/MockInterfaceService.java
index 2367b57..f8d04ca 100644
--- a/apps/segmentrouting/src/test/java/org/onosproject/segmentrouting/MockInterfaceService.java
+++ b/apps/segmentrouting/src/test/java/org/onosproject/segmentrouting/MockInterfaceService.java
@@ -39,4 +39,9 @@
         return interfaces.stream().filter(intf -> cp.equals(intf.connectPoint()))
                 .collect(Collectors.toSet());
     }
+
+    @Override
+    public Set<Interface> getInterfaces() {
+        return interfaces;
+    }
 }