TrashTool: fail if backup object container already exist

This is not supposed to happen and can hide errors.
3 jobs for fix/business_template_update in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-TestRunner1

00:44:38

passed ERP5.PerformanceTest-TestRunner1

00:32:41

failed ERP5.UnitTest-TestRunner1

01:42:02