journalctl,elsewhere: make sure --file=foo fails with sane error msg if foo is not...

journalctl,elsewhere: make sure --file=foo fails with sane error msg if foo is not readable

It annoyed me for quite a while that running "journalctl --file=…" on a
file that is not readable failed with a "File not found" error instead
of a permission error. Let's fix that.

We make this work by using the GLOB_NOCHECK flag for glob() which means
that files are not accessible will be returned in the array as they are
instead of being filtered away. This then means that our later attemps
to open the files will fail cleanly with a good error message.