ux: used new add data sources icon

public/app/features/plugins/partials/ds_list.html

@@ -49,7 +49,7 @@
 	<div ng-if="ctrl.unfiltered.length === 0">
 		<empty-list-cta model="{
 			title: 'There are no data sources defined yet',
-			buttonIcon: 'gicon gicon-dashboard-new',
+			buttonIcon: 'gicon gicon-add-datasources',
 			buttonLink: '/datasources/new',
 			buttonTitle: 'Add data source',
 			proTip: 'You can also define data sources through configuration files.',