test: organize tst_qnetworkreply .pro file a bit

 - Don't run this test in parallel
 - Remove redundant QT=-gui
 - Place the insignificant_test marks together

Change-Id: I078fa29a4dccef9af8798792d06d51835b4b8934
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>