Merge remote-tracking branch 'origin/MAGETWO-84366' into 2.1-develop-pr54

Author: OlgaVasyltsun

app/code/Magento/Ui/view/base/web/js/form/element/file-uploader.js

@@ -304,7 +304,7 @@ define([
 
             if (allowed.passed) {
                 target.on('fileuploadsend', function (event, postData) {
-                    postData.data.set('param_name', this.paramName);
+                    postData.data.append('param_name', this.paramName);
                     $(event.currentTarget).off('fileuploadsend');
                 }.bind(data));