Fix crash in QCombobox when resetting model during currentIndexChanged()

Task-number: QTBUG-20415
Change-Id: Idffc0f29cc55d834c2736ce7562dd7cfe912d327
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Add support for blacklisting test functions

We need to have a finer grained control over the tests
we skip in our CI system. This adds a blacklisting
mechanism that allows blacklisting individual test
functions (or even test data) using a set of predefined
matching keys for the operating system and some other
relevant variables.

QTestlib will search for a file called BLACKLIST in the test
directory and parse it if found. The file contains a simple
ini style list of functions to blacklist. For details see
qtestblacklist.cpp.

Change-Id: Id3fae4b264ca99970cbf9f45bfb85fa75c1fd823
Reviewed-by: Lars Knoll <lars.knoll@digia.com>