tst_QIcon: Mark availableSizes() and task223279_inconsistentAddFile() as XFAIL

Task-number: QTBUG-31993
Change-Id: I10e39951fb38b950633805a44ea4c0edaf55635e
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>