backups: make test config funcs return error

src/apps.js

@@ -1780,10 +1780,11 @@ async function importApp(app, data, auditSource) {
     error = checkAppState(app, exports.ISTATE_PENDING_IMPORT);
     if (error) throw error;
 
-    const testProviderConfig = util.promisify(backups.testProviderConfig);
-
     // TODO: make this smarter to do a read-only test and check if the file exists in the storage backend
-    if (backupConfig) await testProviderConfig(backupConfig);
+    if (backupConfig) {
+        error = await backups.testProviderConfig(backupConfig);
+        if (error) throw error;
+    }
 
     if (backupConfig) {
         if ('password' in backupConfig) {