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.java b/core/api/src/main/java/org/onlab/onos/net/Host.java
index 3a9bfa5..9d08591 100644
--- a/core/api/src/main/java/org/onlab/onos/net/Host.java
+++ b/core/api/src/main/java/org/onlab/onos/net/Host.java
@@ -1,6 +1,6 @@
 package org.onlab.onos.net;
 
-import org.onlab.packet.IpPrefix;
+import org.onlab.packet.IpAddress;
 import org.onlab.packet.MacAddress;
 import org.onlab.packet.VlanId;
 
@@ -38,8 +38,7 @@
      *
      * @return set of IP addresses; empty if no IP address is bound
      */
-    // FIXME: Switch to IpAddress
-    Set<IpPrefix> ipAddresses();
+    Set<IpAddress> ipAddresses();
 
     /**
      * Returns the most recent host location where the host attaches to the