delegate the choice of warehouse

While simulating the procurement, the warehouse was chosen from the
order, which is indeed the standard behaviour. I now delegate the
standard method _prepare_order_line_procurement to choose the warehouse.
That way we get a good simulation also when modules like
sale_sourced_by_line change that behaviour.
Merge remote-tracking branch 'lepistone/8.0_sale_exception_nostock_by_line' into 8.0-test_PRs