backups: split config and policy

keeping them together makes the test/validation quite complicated.
for example, when policy is changed, we test the storage backends

part of #817

src/routes/test/backups-test.js

@@ -23,8 +23,6 @@ describe('Backups API', function () {
                 backupFolder: '/tmp/backups',
                 format: 'tgz',
                 encryption: null,
-                retentionPolicy: { keepWithinSecs: 2 * 24 * 60 * 60 }, // 2 days
-                schedulePattern: '00 00 23 * * *' // every day at 11pm
             });
         });