Implementing region hosts for topology 2

Change-Id: I6d1e45b1152b2387d4ff981dc0666868235eb1c3
diff --git a/core/api/src/main/java/org/onosproject/net/region/RegionStore.java b/core/api/src/main/java/org/onosproject/net/region/RegionStore.java
index 49cc378..a21a1f9 100644
--- a/core/api/src/main/java/org/onosproject/net/region/RegionStore.java
+++ b/core/api/src/main/java/org/onosproject/net/region/RegionStore.java
@@ -17,6 +17,7 @@
 
 import org.onosproject.cluster.NodeId;
 import org.onosproject.net.DeviceId;
+import org.onosproject.net.HostId;
 import org.onosproject.store.Store;
 
 import java.util.Collection;
@@ -110,4 +111,12 @@
      */
     void removeDevices(RegionId regionId, Collection<DeviceId> deviceIds);
 
+    /**
+     * Returns the set of hosts that belong to the specified region.
+     *
+     * @param regionId region identifier
+     * @return set of identifiers for hosts in the given region
+     */
+    Set<HostId> getRegionHosts(RegionId regionId);
+
 }