Adding ability to add simulated hosts to the null provider.

Change-Id: Iaf96caf904e2e8a724064be39211087bf681dad0
diff --git a/providers/null/src/main/java/org/onosproject/provider/nil/CustomTopologySimulator.java b/providers/null/src/main/java/org/onosproject/provider/nil/CustomTopologySimulator.java
index 016b187..a075199 100644
--- a/providers/null/src/main/java/org/onosproject/provider/nil/CustomTopologySimulator.java
+++ b/providers/null/src/main/java/org/onosproject/provider/nil/CustomTopologySimulator.java
@@ -17,11 +17,14 @@
 package org.onosproject.provider.nil;
 
 import com.google.common.collect.Maps;
+import org.onlab.packet.IpAddress;
 import org.onlab.packet.MacAddress;
 import org.onlab.packet.VlanId;
 import org.onosproject.net.Device;
 import org.onosproject.net.DeviceId;
 import org.onosproject.net.HostId;
+import org.onosproject.net.HostLocation;
+import org.onosproject.net.host.DefaultHostDescription;
 
 import java.util.Map;
 
@@ -80,6 +83,19 @@
         nameToId.put(name, id);
     }
 
+    /**
+     * Creates a simulated host.
+     *
+     * @param hostId   host identifier
+     * @param location host location
+     * @param hostIp   host IP address
+     */
+    public void createHost(HostId hostId, HostLocation location, IpAddress hostIp) {
+        DefaultHostDescription description =
+                new DefaultHostDescription(hostId.mac(), hostId.vlanId(), location, hostIp);
+        hostProviderService.hostDetected(hostId, description, false);
+    }
+
     @Override
     protected void createDevices() {
     }