Add failing spec for orders in backend:
Add failing spec for orders in backend:

This adds a failing spec for orders with both:
- A product assembly
- An item that is a product that also belongs to that assembly
Viewing such orders in the backend causes an sql exception due
to the ambiguos semantics of the assemblies_for method in such
contexts.

cindyward1/spree-product-assembly,glossier/spree-product-assembly,groundctrl/spree-product-assembly,TubeDepot/spree_product_assembly,reinaris/spree-product-assembly,groundctrl/spree-product-assembly,agencyleroy/spree-product-assembly,romul/spree-product-assembly,tmedford/spree-product-assembly,helloluis/spree-product-assembly,kimquy/spree-product-assembly,cindyward1/spree-product-assembly,spree-contrib/spree-product-assembly,agencyleroy/spree-product-assembly,surfdome/spree-product-assembly,tmedford/spree-product-assembly,surfdome/spree-product-assembly,glossier/spree-product-assembly,romul/spree-product-assembly,helloluis/spree-product-assembly,kimquy/spree-product-assembly,kimquy/spree-product-assembly,reinaris/spree-product-assembly,agencyleroy/spree-product-assembly,SalzmanGroup/spree-product-assembly,reinaris/spree-product-assembly,surfdome/spree-product-assembly,helloluis/spree-product-assembly,BeDepraved/spree-product-assembly,tmedford/spree-product-assembly,groundctrl/spree-product-assembly,cindyward1/spree-product-assembly,spree-contrib/spree-product-assembly,SalzmanGroup/spree-product-assembly,BeDepraved/spree-product-assembly,BeDepraved/spree-product-assembly,TubeDepot/spree_product_assembly,romul/spree-product-assembly,spree-contrib/spree-product-assembly,glossier/spree-product-assembly