Testcase for Redmine 6569
Support or-entries not evaluated to a scalar

If any entry in an or-list was not evaluated to a scalar, consider it a
"class not set" and evaluate the rest of the entries.

Behavior change for classes promises that use an or constraint where
one of the list entries cannot be evaluated.

Implements redmine 6569
Merge pull request #1990 from vohi/redmine/6569

Redmine/6569