Same as QTBUG-21402, only now tests are disabled directly in qtbase#master. This is necessary because some tests were missed out before qtbase#refactor was integrated into qtbase#master.

Note: This is a temporary measure that needs to be cleaned up as soon as possible. Ideally all disabled tests need to be enabled and passing. All changes will be marked by the string QTBUG-21424 in a comment for easy location.