stub the spree_current_user to make sure there is an admin user for the backend specs.

Signed-off-by: Peter Berkenbosch <peter@pero-ict.nl>
fixing specs that have to deal with proper users and api tokens now.
add spree api tokens to the select2 call and reset the current_user on the product_spec context with custom authorisation.

Signed-off-by: Peter Berkenbosch <peter@pero-ict.nl>