We can do better than just "qmake" and instead take the path to
the qmake that the test was compiled with.
(Can still be overridden with environment variables.)
Change-Id: Icc045d4f96946aeb1f324e6f1334dc9747215f3f
Reviewed-by: Cristian Adam <cristian.adam@qt.io>
Reviewed-by: hjk <hjk@qt.io>