Fixed null providers & custom topo simulator to work across stop/starts.

Change-Id: Id8eeca73c8fc021c351d365ef009b3a95562763a
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 52883a2..e7a5788 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
@@ -122,12 +122,12 @@
     protected void createHosts() {
     }
 
-    /**
-     * Resets the device and host ID seeds to the default values. That is, the
-     * next assigned values will start from 1 again.
-     */
-    public void resetIdSeeds() {
+    @Override
+    public void tearDownTopology() {
+        super.tearDownTopology();
         nextDeviceId = 0;
         nextHostId = 0;
+        nameToId.clear();
     }
+
 }