Add ODKU behavior or delete childs before adding them

[roxblnfk]

product has many productSkus

SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '1-kg' for key 'mt_product_sku.mt_product_sku_index_product_id_attribute_name_61a108014425b'   
(1-kg ,"1" is product id and "kg" is attribute name)

string(194) "INSERT INTO `mt_product_sku` (`sequence`, `status`, `created_at`, `updated_at`, `ip_address`, `product_id`, `attribute_name`, `weight`, `price`, `quantity`) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)"

the right action should be delete the same rows or ON DUPLICATE KEY UPDATE

Originally posted by @TiaNex-Com in #342