fix #1528 by removing PYTHONPATH before pyenv exec
fix #1528 by removing PYTHONPATH before pyenv exec

mrakitin/sirepo,radiasoft/sirepo,radiasoft/sirepo,mkeilman/sirepo,mkeilman/sirepo,radiasoft/sirepo,mrakitin/sirepo,radiasoft/sirepo,mkeilman/sirepo,mrakitin/sirepo,mrakitin/sirepo,radiasoft/sirepo,mkeilman/sirepo