Fixes the test for width of condensed fonts so it doesn't depend
on the presence of the Liberation font on the system, and adds
another test that condensed sub-families can be matched
consistently. The latter will however not work on Windows until
QTBUG-53458 is solved.
Task-number: QTBUG-51335.
Change-Id: Id6d046274fa21b2dce0ad6b32dce7f1c8a92a4f4
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>
