Fix "assert_called_once_with" depending on list's order
Fix "assert_called_once_with" depending on list's order

The `update_products_minimal_variant_prices_task` accepts list
of product ids which order varies:

https://travis-ci.com/mirumee/saleor/jobs/265209511

maferelo/saleor,maferelo/saleor,mociepka/saleor,mociepka/saleor,maferelo/saleor,mociepka/saleor