[Qemu-block] hd-geo-test creates 4GB files on FSes that don't support sparse images, doesn't delete them on error

[Peter Maydell]

I've noticed recently that tests/hd-geo-test.c creates test disk
images which are 4GB in size, which is a problem if the filesystem
on the host doesn't support sparse files. In particular, OSX's HFS+
doesn't have sparse file support, and Windows probably doesn't either.
Worse, if the test fails an assertion somewhere the test doesn't
clean up after itself and leaves a 4GB file lying around in /tmp/.

It would be nice if we could skip these tests on filesystems that
don't have sparse file support...

thanks
-- PMM