Use information provided by the codemodel and the run configurations
as much as possible to avoid guessing.
This also fixes running CMake based tests from within the
AutoTest plugin.

Task-number: QTCREATORBUG-17882
Change-Id: I5639fa947fa602b76faf50e9b58d7a74af4e1f9c
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>