test: Adapt to Qt.platform.os rename ("mac" -> "osx")

Marking this test as QSKIP and also updating the JIRA task

Task-number: QTBUG-32650
Change-Id: I9e98024bf50c43f96269c39d779803ae9c46168d
Reviewed-by: Simo Fält <simo.falt@digia.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>