ONOS-4326: Focusing on add/remove cluster member. (WIP).

If reviewing this, please refer to http://tinyurl.com/onos-ui-topo-model

Change-Id: Ic6568074ac768ec828f9103e92caab5e9a06ade6
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java
index 78f9d47..88d86d0 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java
@@ -17,6 +17,7 @@
 package org.onosproject.ui.model.topo;
 
 import org.onosproject.net.Device;
+import org.onosproject.net.DeviceId;
 
 /**
  * Represents a device.
@@ -29,4 +30,18 @@
     protected void destroy() {
         device = null;
     }
+
+    /**
+     * Returns the identity of the device.
+     *
+     * @return device ID
+     */
+    public DeviceId id() {
+        return device.id();
+    }
+
+    @Override
+    public String idAsString() {
+        return id().toString();
+    }
 }