Topo2: Bug fixes
1: port lables not showing on mouseover
2: D3 Errors when there are no topology errors and a user pans/zooms

Change-Id: Ic65ba393d23b60673c3a731d1986ee15bbe1bd88
diff --git a/web/gui/src/main/webapp/app/view/topo2/topo2Link.js b/web/gui/src/main/webapp/app/view/topo2/topo2Link.js
index be8d03c..e644c7c 100644
--- a/web/gui/src/main/webapp/app/view/topo2/topo2Link.js
+++ b/web/gui/src/main/webapp/app/view/topo2/topo2Link.js
@@ -174,7 +174,7 @@
                         data.push(point);
                     }
 
-                    var entering = d3.select('#topo2-portLabels')
+                    var entering = d3.select('.topo2-portLabels')
                         .selectAll('.portLabel')
                         .data(data)
                         .enter().append('g')
@@ -204,7 +204,7 @@
             },
             unenhance: function () {
                 this.set('enhanced', false);
-                d3.select('#topo2-portLabels').selectAll('.portLabel').remove();
+                d3.select('.topo2-portLabels').selectAll('.portLabel').remove();
             },
             getSelected: function () {
                 return this.collection.filter(function (m) {