Log output of optipng when it fails

[Martchus]

• Remove the -quiet parameter
• Use run_cmd_with_log_return_error for logging the command output in the error case
• Improve error messages in run_cmd_with_log_return_error to include the program name so the error message is also useful on its own (without the prior Running cmd: … message)
• Make run_cmd_with_log_return_error return the error message so it can be passed as reason when using it to run optipng
• See https://progress.opensuse.org/issues/190920

[Martchus]

It looks like using the IPC run-based run_cmd_with_log_return_error cannot be used here - at least not without further modification. The problem is that when run_cmd_with_log_return_error is used after call_driver (like we do in fullstack tests) the $? variable doesn't return the correct value. And also the return value of IPC::Run::run(…) is false when it should be true.

Unless somebody has an idea how to fix this I probably would have to extend the current custom code for starting optipng to make this work. Maybe it would be similar to how I implemented it in the scripts repo but here we would also need to cover stderr (via e.g. 2>&1).

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏