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/HostStore.java b/core/api/src/main/java/org/onlab/onos/net/host/HostStore.java
index b27b697..535479c8 100644
--- a/core/api/src/main/java/org/onlab/onos/net/host/HostStore.java
+++ b/core/api/src/main/java/org/onlab/onos/net/host/HostStore.java
@@ -6,7 +6,7 @@
 import org.onlab.onos.net.HostId;
 import org.onlab.onos.net.provider.ProviderId;
 import org.onlab.onos.store.Store;
-import org.onlab.packet.IpPrefix;
+import org.onlab.packet.IpAddress;
 import org.onlab.packet.MacAddress;
 import org.onlab.packet.VlanId;
 
@@ -82,8 +82,7 @@
      * @param ip ip address
      * @return set of hosts with the given IP
      */
-    // FIXME: Switch to IpAddress
-    Set<Host> getHosts(IpPrefix ip);
+    Set<Host> getHosts(IpAddress ip);
 
     /**
      * Returns the set of hosts whose location falls on the given connection point.