Let config_parse open file where applicable

Special care is needed so that we get an error message if the
file failed to parse, but not when it is missing. To avoid duplicating
the same error check in every caller, add an additional 'warn' boolean
to tell config_parse whether a message should be issued.
This makes things both shorter and more robust wrt. to error reporting.
Be more careful when checking for empty files

If we want to avoid reading a totally empty file, it seems better
to check after we have opened the file, not before.
tty-ask-password-agent: modernization
test-tables: add new entries

One missing string found.

A few things had to be moved around to make it possible to test them.
journal/verify: flush progress bar, print offset in more places

Before, fragments of the progress bar would remain when
errors or warnings were printed.