Don't leave fds created with --log-file, --xml-file or --log-socket open

Don't leave fds created with --log-file, --xml-file or --log-socket open

prepare_sink_fd and prepare_sink_socket will create a new file
descriptor for the output sink. finalize_sink_fd then copies the fd
to the safe range, so it doesn't conflict with any application fds.

If we created the original fd ourselves, it was a VgLogTo_File or
VgLogTo_Socket, not VgLogTo_Fd, finalize_sink_fd should close it.

Also close socket when connecting fails in VG_(connect_via_socket).

Add a testcase for --log-file and --xml-file which prints output to
/dev/stderr

https://bugs.kde.org/show_bug.cgi?id=202770
https://bugs.kde.org/show_bug.cgi?id=311655
https://bugs.kde.org/show_bug.cgi?id=488379

Co-authored-by: Alexandra Hájková <ahajkova@redhat.com