add test which checks the property types

Summary:
Check the type of the properties defined in kfilemetadata vs. the actual returned types obtained from QVariant.
Testing only one file is sufficient as this is shared code. Expected failures are declared as such.

Reviewers: mgallien, bruns

Subscribers: kde-frameworks-devel, Baloo

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D12950