Apply import defaults to variants of new products
Apply import defaults to variants of new products

Spree 2 doesn't have `Product#on_hand=` any more. We actually can't save
stock levels without saving the product first which creates a stock
item.

This hacky solution overwrites the attribute in the entry so that it
gets copied to the variant later on. I think a better solution needs
some refactoring as proposed in:
https://github.com/openfoodfoundation/openfoodnetwork/issues/2783#issuecomment-459601530

mkllnk/openfoodnetwork,openfoodfoundation/openfoodnetwork,lin-d-hop/openfoodnetwork,openfoodfoundation/openfoodnetwork,Matt-Yorkley/openfoodnetwork,lin-d-hop/openfoodnetwork,Matt-Yorkley/openfoodnetwork,lin-d-hop/openfoodnetwork,Matt-Yorkley/openfoodnetwork,openfoodfoundation/openfoodnetwork,mkllnk/openfoodnetwork,lin-d-hop/openfoodnetwork,mkllnk/openfoodnetwork,mkllnk/openfoodnetwork,Matt-Yorkley/openfoodnetwork,openfoodfoundation/openfoodnetwork