Add uptimes to device and cluster REST APIs

Change-Id: I0ccdf4e33135be4bcfd1674a76ff4b39e992268b
diff --git a/core/api/src/main/java/org/onosproject/net/device/DeviceService.java b/core/api/src/main/java/org/onosproject/net/device/DeviceService.java
index 232809b..f86a98a 100644
--- a/core/api/src/main/java/org/onosproject/net/device/DeviceService.java
+++ b/core/api/src/main/java/org/onosproject/net/device/DeviceService.java
@@ -185,4 +185,14 @@
      */
     String localStatus(DeviceId deviceId);
 
+
+    /**
+     * Indicates how long ago the device connected or disconnected from this
+     * controller instance as a time offset.
+     *
+     * @param deviceId device identifier
+     * @return time offset in miliseconds
+     */
+    long getLastUpdatedInstant(DeviceId deviceId);
+
 }