ONOS-4326: Working on topology topo2start processing.
- Added getPeers() to UiTopoLayoutService.
- Fixed wipe-out command to leave the default layout alone.
- Fixed handling of null-region (associated with default layout).
- Added refresh() method to model cache.
- Fixed regions-topo-2 device IDs

Change-Id: Iee49b47ff6702bed9751be7b63392577422d4763
diff --git a/core/api/src/main/java/org/onosproject/ui/UiTopoLayoutService.java b/core/api/src/main/java/org/onosproject/ui/UiTopoLayoutService.java
index 0f2c273..287cc43 100644
--- a/core/api/src/main/java/org/onosproject/ui/UiTopoLayoutService.java
+++ b/core/api/src/main/java/org/onosproject/ui/UiTopoLayoutService.java
@@ -57,6 +57,15 @@
     UiTopoLayout getLayout(UiTopoLayoutId layoutId);
 
     /**
+     * Returns the set of peer layouts of the specified layout. That is,
+     * those layouts that share the same parent.
+     *
+     * @param layoutId layout identifier
+     * @return set of peer layouts; empty set if layout has no peers
+     */
+    Set<UiTopoLayout> getPeers(UiTopoLayoutId layoutId);
+
+    /**
      * Returns the set of the child layouts of the specified layout.
      *
      * @param layoutId layout identifier