AMBARI-3084. align middle the caret on host component expander. (Jeff Sposetti via yusaku)

ambari-web/app/styles/application.less

@@ -2693,6 +2693,7 @@ table.graphs {
     .caret {
       vertical-align: middle;
       margin-right: 5px;
+      margin-bottom: 2px;
       &.right {
         border-left: 4px solid #000000;
         border-top: 4px solid transparent;