Add CLI command to view groups on switches

Change-Id: I0ce3cca85e8b38d2e713bf1f0abd4303629e15e4
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupService.java b/core/api/src/main/java/org/onosproject/net/group/GroupService.java
index 8502aea..cdd56c7 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupService.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupService.java
@@ -127,6 +127,14 @@
     Iterable<Group> getGroups(DeviceId deviceId, ApplicationId appId);
 
     /**
+     * Returns all groups associated with the given device.
+     *
+     * @param deviceId device ID to get groups for
+     * @return iterable of device's groups
+     */
+    Iterable<Group> getGroups(DeviceId deviceId);
+
+    /**
      * Adds the specified group listener.
      *
      * @param listener group listener