[krbdev.mit.edu #8377] Improve message "kdb5_util: Configuration file does not specify default realm while getting default realm"

[Karl-Philipp Richter via RT]

It'd be much more helpful if the error `kdb5_util` error message
`kdb5_util: Configuration file does not specify default realm while
getting default realm` would contain the path of the configuration file,
i.e. `kdb5_util: Configuration file '/absolute/path/to/file' does not
specify default realm while getting default realm`.

experienced with 0533ebf