backup tests corrected (nc-215)
method delete_instance_backups was renamed to delete_instance_backup (nc-215)
merge with current develop (nc-215)
Merge branch 'feature/nc-215' into 'develop'

Feature/nc 215

Backup tests were corrected. Field result_id was removed from Backup model (it was unused). Method delete_instance_backups renamed to delete_instance_backup