To avoid (even more) duplicated code, "qt_test_helper" ensures the
policy of putting a test's helper application next to the test's
own executable.
The helper executable is suffixed with "_helper" to avoid name
clashes with its folder.
Change-Id: Ic50cb1daa257e7ffc75440c10a3b90fd39424683
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
