Include attribute code in error message

[lazyguru]

Description

The error message during import of a configurable product(s) is slightly vague if the configurable product(s) contain multiple super attributes

Manual testing scenarios

1. Create an import file that would create a configurable product with more than one attribute set to be a super attribute (ensure that one of the attributes is not actually setup properly for use as a super attribute. eg type=text or attribute not included in attribute_set)
2. Attempt to import the file

Before

Error message reads: Attribute with this code is not super in rows: 1, 2, 3...

After

Error message reads: Attribute with code "color" is not super in rows: 1, 2, 3...