ZDC: Change exit code for failure of python scripts

This merge requests simply changes the exit code from -1 to 1 in case of failure for python scripts in ZDC code, such that PanDA can detect when these scripts fail.

Exiting from python scripts with exit code -1 is problematic with grid submissions. When executing a python script (e.g., python -m ...), an exit code of -1 becomes 255 (e.g., if one checks with echo $?). When PanDA checks the exit status of scripts submitted with prun, it takes the exit code modulo 255 (examples). Thus, jobs executing such scripts will always appear to succeed.