Functional tests for the product reference field

We need tests for the product reference field:

• Create a product reference field
• Attach it to a node
• Attach it to a user
• Reference products
• Test the "limit the referencable types" feature
• Test the display of fields pulled from the product
• Test the SKU (link) formatter
• Test the SKU (no link) formatter
• Test the Title (link) formatter
• Test the Title (no link) formatter