Revert "IOError handling for _read_conf_file function"

This reverts commit 79b5e468934ad0a9cca7eb2a3b8ec2baead21317.
Provider an `is_readable` path validator.
Don't just check for an existing file.

The file might exist, we just might not be able to read it.
Refs #11783.
Merge pull request #11892 from s0undt3ch/hotfix/improved-exit

Don't trace on IOErrors