Address comments in gerrit 20328

Create a new class XconnecEndpoint to cover both physical port and load balancer
Also change the CLI load balancer identifier to "LB:"

Change-Id: I0b4cd6e474d8b21468d87fcadd9280fdf7d6aafa
diff --git a/web/src/main/java/org/onosproject/segmentrouting/web/XconnectWebResource.java b/web/src/main/java/org/onosproject/segmentrouting/web/XconnectWebResource.java
index edaea9e..51c9cc9 100644
--- a/web/src/main/java/org/onosproject/segmentrouting/web/XconnectWebResource.java
+++ b/web/src/main/java/org/onosproject/segmentrouting/web/XconnectWebResource.java
@@ -75,12 +75,12 @@
         ObjectNode json = readTreeFromStream(mapper, input);
         XconnectDesc desc = codec(XconnectDesc.class).decode(json, this);
 
-        if (desc.ports().size() != 2) {
+        if (desc.endpoints().size() != 2) {
             throw new IllegalArgumentException("Ports should have only two items.");
         }
 
         XconnectService xconnectService = get(XconnectService.class);
-        xconnectService.addOrUpdateXconnect(desc.key().deviceId(), desc.key().vlanId(), desc.ports());
+        xconnectService.addOrUpdateXconnect(desc.key().deviceId(), desc.key().vlanId(), desc.endpoints());
 
         return Response.ok().build();
     }