Topology REST API modifications and unit tests

- added a Serializer for Topology operations
- added a REST test harness class for Topology tests
- added REST API tests for topology get of all
  topology, links, switches, and devices.

Change-Id: I13e3654aad7c0f5af41f07be66da82330933d3a3
diff --git a/src/main/java/net/onrc/onos/core/topology/Topology.java b/src/main/java/net/onrc/onos/core/topology/Topology.java
index 3b90f89..844507d 100644
--- a/src/main/java/net/onrc/onos/core/topology/Topology.java
+++ b/src/main/java/net/onrc/onos/core/topology/Topology.java
@@ -1,12 +1,15 @@
 package net.onrc.onos.core.topology;
 
 import net.floodlightcontroller.util.MACAddress;
+import net.onrc.onos.core.topology.serializers.TopologySerializer;
+import org.codehaus.jackson.map.annotate.JsonSerialize;
 
 /**
  * The northbound interface to the topology. This interface
  * is presented to the rest of ONOS. It is currently read-only, as we want
  * only the discovery modules to be allowed to modify the topology.
  */
+@JsonSerialize(using = TopologySerializer.class)
 public interface Topology {
     /**
      * Get the switch for a given switch DPID.