cmake: Fix a way to get a python version (for Python 2.6)
cmake: Fix a way to get a python version (for Python 2.6)

cgwalters/librepo,Conan-Kudo/librepo,bgamari/librepo,cgwalters/librepo,Tojaj/librepo,Conan-Kudo/librepo,Tojaj/librepo,Conan-Kudo/librepo,rpm-software-management/librepo,cgwalters/librepo,bgamari/librepo,Tojaj/librepo,rpm-software-management/librepo,rholy/librepo,rholy/librepo,rholy/librepo,rholy/librepo,cgwalters/librepo,bgamari/librepo,rpm-software-management/librepo