tst_qfiledialog: extend reject-test to test getOpenFileNames etc.

So that this method is at least called once in the test :)

Change-Id: I3b5fc6b7c464d9e56264c709cfa313d475004207
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
tst_qfiledialog: ease debugging of "directoryEntered not emitted".

It can happen when the sidebar only has only one item, due to
"My Computer" being missing.

Change-Id: I2b38fef45139f1dfa20d88059e56185c3163a833
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>