apply backup retention policy

part of #441

src/routes/test/backups-test.js

@@ -62,7 +62,7 @@ function setup(done) {
         },
 
         function createSettings(callback) {
-            settings.setBackupConfig({ provider: 'filesystem', backupFolder: '/tmp', format: 'tgz' }, callback);
+            settings.setBackupConfig({ provider: 'filesystem', backupFolder: '/tmp', format: 'tgz', retentionPolicy: {} }, callback);
         }
     ], done);
 }