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/core/api/src/test/java/org/onlab/onos/net/NetTestTools.java b/core/api/src/test/java/org/onlab/onos/net/NetTestTools.java
index 6fc38e3..1d2e1af 100644
--- a/core/api/src/test/java/org/onlab/onos/net/NetTestTools.java
+++ b/core/api/src/test/java/org/onlab/onos/net/NetTestTools.java
@@ -2,7 +2,7 @@
 
 import org.onlab.onos.net.provider.ProviderId;
 import org.onlab.packet.ChassisId;
-import org.onlab.packet.IpPrefix;
+import org.onlab.packet.IpAddress;
 
 import java.util.ArrayList;
 import java.util.HashSet;
@@ -45,7 +45,7 @@
     public static Host host(String id, String did) {
         return new DefaultHost(PID, hid(id), valueOf(1234), vlanId((short) 2),
                                new HostLocation(did(did), portNumber(1), 321),
-                               new HashSet<IpPrefix>());
+                               new HashSet<IpAddress>());
     }
 
     // Short-hand for creating a connection point.