Replaced IpPrefix and IpAddress in the following methods
and cleanup related code:

 - Host.ipAddresses()
 - DefaultHost.ipAddresses()
 - HostDescription.ipAddress()
 - DefaultHostDescription.ipAddress()
 - HostService.getHostsByIp()
 - HostManager.getHostsByIp()
 - HostStore.getHosts()
 - GossipHostStore.getHosts()
 - SimpleHostStore.getHosts()
 - ProxyArpService.known()
 - ProxyArpManager.known()

As a result of the above cleanup, the "hosts" CLI command outputs
the IP addresses as "1.2.3.4" instead of "1.2.3.4/32".

Also, the following REST calls might be affected as well with
the above format replacement:
  - REST POST: config/topology
  - REST GET: topology/graph
diff --git a/apps/sdnip/src/main/java/org/onlab/onos/sdnip/Router.java b/apps/sdnip/src/main/java/org/onlab/onos/sdnip/Router.java
index 0907cd6..4e3415b 100644
--- a/apps/sdnip/src/main/java/org/onlab/onos/sdnip/Router.java
+++ b/apps/sdnip/src/main/java/org/onlab/onos/sdnip/Router.java
@@ -520,8 +520,7 @@
 
         // See if we know the MAC address of the next hop
         MacAddress nextHopMacAddress = null;
-        Set<Host> hosts = hostService.getHostsByIp(
-                routeEntry.nextHop().toPrefix());
+        Set<Host> hosts = hostService.getHostsByIp(routeEntry.nextHop());
         if (!hosts.isEmpty()) {
             // TODO how to handle if multiple hosts are returned?
             nextHopMacAddress = hosts.iterator().next().mac();
@@ -773,8 +772,8 @@
             if (event.type() == HostEvent.Type.HOST_ADDED ||
                     event.type() == HostEvent.Type.HOST_UPDATED) {
                 Host host = event.subject();
-                for (IpPrefix ip : host.ipAddresses()) {
-                    updateMac(ip.toIpAddress(), host.mac());
+                for (IpAddress ip : host.ipAddresses()) {
+                    updateMac(ip, host.mac());
                 }
             }
         }