[ONOS-4681] Enables device registration in GossipDeviceStore,
exposes availability, and polls NETCONF device reachability.

Change-Id: I5492c7b6109c3431d71555a9104c7e97fc6e75be
diff --git a/core/common/src/test/java/org/onosproject/store/trivial/SimpleDeviceStore.java b/core/common/src/test/java/org/onosproject/store/trivial/SimpleDeviceStore.java
index 31b4292..b51a1d1 100644
--- a/core/common/src/test/java/org/onosproject/store/trivial/SimpleDeviceStore.java
+++ b/core/common/src/test/java/org/onosproject/store/trivial/SimpleDeviceStore.java
@@ -245,6 +245,13 @@
         }
     }
 
+    // implement differently if desired
+    @Override
+    public boolean markOnline(DeviceId deviceId) {
+        log.warn("Mark online not supported");
+        return false;
+    }
+
     @Override
     public List<DeviceEvent> updatePorts(ProviderId providerId,
                                          DeviceId deviceId,