Since some GUI event dispatchers are complete reimplementations and do
not build on the corelib ones, we want to run the same tests with the
other dispatcher.
Since this is a GUI test now, we need to make sure to drain system
events queued during application startup to make sure we can reliably
run the test functions.
Change-Id: I4905db70bc8f8584c4ef1f4d767824040281452c
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
