Make category query compatible with staging

[paliarush]

Preconditions

1. Magento Commerce is installed (not just open source)
2. At least one category in the system has a scheduled update

Steps to reproduce

1. Create a new category
2. Request this category by ID via GraphQL API:

{
  category(id: 4) {
    name
    products(sort: {sku: ASC}) {
      total_count
      items {
        sku
      }
    }
  }
}

Expected result

1. Requested category info should be returned in the result

Actual result

1. Category in the response is null

Additional info

• Possible fix is to replace getLinkField() with getIdentifierField() here.
• Existing tests should be adjusted. At least this one \Magento\GraphQl\Catalog\CategoryTest::testAnchorCategory

[naydav]

#99