Extend host structures to store multiple locations

Also update host location format in CLI and REST API

Change-Id: I0fbd655f642627dd3eb8a2925f83a3ee016fe4aa
diff --git a/core/api/src/main/java/org/onosproject/net/HostLocation.java b/core/api/src/main/java/org/onosproject/net/HostLocation.java
index f7868c6..94409b6 100644
--- a/core/api/src/main/java/org/onosproject/net/HostLocation.java
+++ b/core/api/src/main/java/org/onosproject/net/HostLocation.java
@@ -64,4 +64,8 @@
         return time;
     }
 
+    @Override
+    public String toString() {
+        return deviceId() + "/" + port();
+    }
 }