iotests: Improve iotest 194 to mirror data

Mirroring a completely sparse image to a sparse destination should be
practically instantaneous.  It isn't yet, but the test will be more
realistic if it has some non-zero to mirror as well as the holes.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20250509204341.3553601-20-eblake@redhat.com>
1 file changed