journald: when we are asked to rotate all files, let's also look at closed files

journald: when we are asked to rotate all files, let's also look at closed files

Before this when asked for rotation we'd only rotate files we have open
anyway. However there might be a number of other files on disk that are
active (i.e. not archived yet) but not open. Let's take care of those
too, so that rotation is always comprehensive, and the user gets the
guarantee that afterthe rotation all stored data is in archived files.

Fixes: #1017