Formalized HostStore in preparation for separating managers and stores.
diff --git a/core/trivial/src/test/java/org/onlab/onos/net/trivial/host/impl/SimpleHostManagerTest.java b/core/trivial/src/test/java/org/onlab/onos/net/trivial/host/impl/SimpleHostManagerTest.java
index 67c14b0..1ee61df 100644
--- a/core/trivial/src/test/java/org/onlab/onos/net/trivial/host/impl/SimpleHostManagerTest.java
+++ b/core/trivial/src/test/java/org/onlab/onos/net/trivial/host/impl/SimpleHostManagerTest.java
@@ -73,6 +73,7 @@
     @Before
     public void setUp() {
         mgr = new SimpleHostManager();
+        mgr.store = new SimpleHostStore();
         mgr.eventDispatcher = new TestEventDispatcher();
         registry = mgr;
         mgr.activate();