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/host/HostEventTest.java b/core/api/src/test/java/org/onlab/onos/net/host/HostEventTest.java
index 92a5718..561b041 100644
--- a/core/api/src/test/java/org/onlab/onos/net/host/HostEventTest.java
+++ b/core/api/src/test/java/org/onlab/onos/net/host/HostEventTest.java
@@ -11,7 +11,7 @@
 import org.onlab.onos.net.HostLocation;
 import org.onlab.onos.net.PortNumber;
 import org.onlab.onos.net.provider.ProviderId;
-import org.onlab.packet.IpPrefix;
+import org.onlab.packet.IpAddress;
 import org.onlab.packet.MacAddress;
 import org.onlab.packet.VlanId;
 
@@ -27,9 +27,9 @@
                     PortNumber.portNumber(100),
                     123L
                 );
-        Set<IpPrefix> ipset = Sets.newHashSet(
-                    IpPrefix.valueOf("10.0.0.1"),
-                    IpPrefix.valueOf("10.0.0.2")
+        Set<IpAddress> ipset = Sets.newHashSet(
+                    IpAddress.valueOf("10.0.0.1"),
+                    IpAddress.valueOf("10.0.0.2")
                 );
         HostId hid = HostId.hostId(mac, vlan);