Fix containerd fails to pull OCI image with non-http(s):// urls

Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>
(cherry picked from commit 526defb)
Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>

Author: ktock

remotes/docker/fetcher.go

@@ -60,6 +60,10 @@ func (r dockerFetcher) Fetch(ctx context.Context, desc ocispec.Descriptor) (io.R
 				log.G(ctx).WithError(err).Debug("failed to parse")
 				continue
 			}
+			if u.Scheme != "http" && u.Scheme != "https" {
+				log.G(ctx).Debug("non-http(s) alternative url is unsupported")
+				continue
+			}
 			log.G(ctx).Debug("trying alternative url")
 
 			// Try this first, parse it