Implementing region hosts for topology 2

Change-Id: I6d1e45b1152b2387d4ff981dc0666868235eb1c3
diff --git a/core/api/src/main/java/org/onosproject/net/region/RegionService.java b/core/api/src/main/java/org/onosproject/net/region/RegionService.java
index 259c8b0..b2b9b14 100644
--- a/core/api/src/main/java/org/onosproject/net/region/RegionService.java
+++ b/core/api/src/main/java/org/onosproject/net/region/RegionService.java
@@ -18,6 +18,7 @@
 
 import org.onosproject.event.ListenerService;
 import org.onosproject.net.DeviceId;
+import org.onosproject.net.HostId;
 
 import java.util.Set;
 
@@ -59,4 +60,12 @@
      */
     Set<DeviceId> getRegionDevices(RegionId regionId);
 
+    /**
+     * 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);
+
 }