Just starting 20 threads to test this won't cut it if
the machine you're testing on has an ideal thread count
of 16 or larger.
Change-Id: Icba8f00aa836fec6da41c71b318e9e17bdd47c0e
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>