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/cli/src/main/java/org/onlab/onos/cli/net/HostsListCommand.java b/cli/src/main/java/org/onlab/onos/cli/net/HostsListCommand.java
index 0265116..ab7a1f3 100644
--- a/cli/src/main/java/org/onlab/onos/cli/net/HostsListCommand.java
+++ b/cli/src/main/java/org/onlab/onos/cli/net/HostsListCommand.java
@@ -27,7 +27,7 @@
 import org.onlab.onos.cli.Comparators;
 import org.onlab.onos.net.Host;
 import org.onlab.onos.net.host.HostService;
-import org.onlab.packet.IpPrefix;
+import org.onlab.packet.IpAddress;
 
 import java.util.Collections;
 import java.util.List;
@@ -71,7 +71,7 @@
         ObjectNode loc = LinksListCommand.json(mapper, host.location())
                 .put("time", host.location().time());
         ArrayNode ips = mapper.createArrayNode();
-        for (IpPrefix ip : host.ipAddresses()) {
+        for (IpAddress ip : host.ipAddresses()) {
             ips.add(ip.toString());
         }
         ObjectNode result = mapper.createObjectNode()