panel: add baron scroller to correct element

This resolves issue with alert list panel getting scrollbars
attached to incorrect element. Now the panel content are
rendered correctly and all content are displayed as
expected.

public/app/features/panel/panel_directive.ts

@@ -113,7 +113,8 @@ module.directive('grafanaPanel', function($rootScope, $document, $timeout) {
           `;
 
           let scrollRoot = panelContent;
-          let scroller = panelContent.find(':first-child').find(':first-child');
+          let scroller = panelContent.find(':first').find(':first');
+
           scrollRoot.addClass(scrollRootClass);
           $(scrollBarHTML).appendTo(scrollRoot);
           scroller.addClass(scrollerClass);