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/main/java/org/onlab/onos/net/host/HostDescription.java b/core/api/src/main/java/org/onlab/onos/net/host/HostDescription.java
index 258ce3d..c42dc03 100644
--- a/core/api/src/main/java/org/onlab/onos/net/host/HostDescription.java
+++ b/core/api/src/main/java/org/onlab/onos/net/host/HostDescription.java
@@ -4,7 +4,7 @@
 
 import org.onlab.onos.net.Description;
 import org.onlab.onos.net.HostLocation;
-import org.onlab.packet.IpPrefix;
+import org.onlab.packet.IpAddress;
 import org.onlab.packet.MacAddress;
 import org.onlab.packet.VlanId;
 
@@ -39,7 +39,5 @@
      *
      * @return host IP address
      */
-    // FIXME: Switch to IpAddress
-    Set<IpPrefix> ipAddress();
-
+    Set<IpAddress> ipAddress();
 }