Exit status codes mixed up

# Description
The exit status codes of OFT don't comply with `usage.txt` which says.

> Returns:
>  0   on success
>  1   on OFT error
>  2   on command line error

## Steps to Reproduce
1. Enter illegal command line option
2. Check exit code

## Expected behavior
See above.

# Environment
- OFT: 2.2.0

## Additional context
This is a finding from a review of @poldi2015.
