Adding more unit tests.
Made some classes abstract which should have been.
diff --git a/core/api/src/main/java/org/onlab/onos/net/DefaultHost.java b/core/api/src/main/java/org/onlab/onos/net/DefaultHost.java
index efa876b..85712e8 100644
--- a/core/api/src/main/java/org/onlab/onos/net/DefaultHost.java
+++ b/core/api/src/main/java/org/onlab/onos/net/DefaultHost.java
@@ -45,7 +45,7 @@
 
     @Override
     public HostId id() {
-        return (HostId) super.id();
+        return (HostId) id;
     }
 
     @Override