tst_qtabbar uses fixed values to check the minimumSizeHint and it fails
with screens that have a higher resolution. The test still uses the
default values, but now in the beginning it creates enough tabs so that
it goes over the default.

Change-Id: I3f891d2661288d7fad50ad522d73f634b3e91958
Reviewed-by: Andy Shaw <andy.shaw@theqtcompany.com>