Add backup download route if backend supports it

src/storage/filesystem.js

@@ -5,6 +5,7 @@ exports = module.exports = {
     getAppBackupDetails: getAppBackupDetails,
 
     getRestoreUrl: getRestoreUrl,
+    getLocalFilePath: getLocalFilePath,
 
     copyObject: copyObject
 };
@@ -56,6 +57,16 @@ function getRestoreUrl(apiConfig, filename, callback) {
     callback(null, { url: restoreUrl });
 }
 
+function getLocalFilePath(apiConfig, filename, callback) {
+    assert.strictEqual(typeof apiConfig, 'object');
+    assert.strictEqual(typeof filename, 'string');
+    assert.strictEqual(typeof callback, 'function');
+
+    var backupFolder = apiConfig.backupFolder || FALLBACK_BACKUP_FOLDER;
+
+    callback(null, { filePath: path.join(backupFolder, filename) });
+}
+
 function copyObject(apiConfig, from, to, callback) {
     assert.strictEqual(typeof apiConfig, 'object');
     assert.strictEqual(typeof from, 'string');