Cleanup: restructure bash script cleanup process

Cleanup: restructure bash script cleanup process

Explicitly return 0 in main.

The cleanup function can be called within the functions being removed.
This is handy in that the cleanup no longer has to be called after the main function.
The error code can then be properly returned without being lost due to the cleanup function.
Once this is done, return can be used instead of exit (which is generally safer).