data export: Fix success banner not clearing.

There was a bug where the success banner stuck
around even after the export completed.  We now
nicely fade and remove the banner upon a successful
population of the export in the table.

Fixes: #13045

frontend_tests/node_tests/dispatch.js

@@ -60,6 +60,7 @@ set_global('settings_exports', {
     populate_exports_table: function (exports) {
         return exports;
     },
+    clear_success_banner: noop,
 });
 
 // page_params is highly coupled to dispatching now

static/js/server_events_dispatch.js

@@ -512,6 +512,7 @@ exports.dispatch_normal_event = function dispatch_normal_event(event) {
         break;
     case 'realm_export':
         settings_exports.populate_exports_table(event.exports);
+        settings_exports.clear_success_banner();
         break;
     }
 

static/js/settings_exports.js

@@ -12,6 +12,18 @@ exports.reset = function () {
     meta.loaded = false;
 };
 
+exports.clear_success_banner = function () {
+    var export_status = $('#export_status');
+    if (export_status.hasClass('alert-success')) {
+        // Politely remove our success banner if the export
+        // finishes before the view is closed.
+        export_status.fadeTo(200, 0);
+        setTimeout(function () {
+            export_status.hide();
+        }, 205);
+    }
+};
+
 exports.populate_exports_table = function (exports) {
     if (!meta.loaded) {
         return;