CORSIKA exit code is alway zero

Just to let you know, I learned that the proper way to test if a corsika run was successfull is to check that there is the line:

```
== END OF RUN ==
```
in the log.

E.g.:
```python
if '== END OF RUN ==' not in corsika_log:
    log.error('== END OF RUN== not in CORSIKA log output')
    log.error('CORSIKA did not finish successfully')
    sys.exit(1)

```