ci: Don't re-upload reference images every time

ci/piglit: Use wget instead of ci-fairy to check a file exists

ci-fairy minio ls will try to list files in the path given, which for trace buckets is generally forbidden. We don't really need to do any listing in this case, so use wget instead to check that the reference image doesn't exist yet.

Previous to this patch, trace jobs would re-upload all reference images to minio every time because they wouldn't be able to verify that the reference image was already there. Jobs would often take up to 4 minutes needlessly re-uploading these files.

Signed-off-by: Tomeu Vizoso tomeu.vizoso@collabora.com