Enable fetching and uploading images using HTTP protocol

Stargzifying an image on a HTTP registry fails when the registry isn't
"localhost"(or 127.0.0.1).
Recently, go-containerregistry supported to read/write images using HTTP even
for fat images. (google/go-containerregistry#567)
So we can introduce "insecure" options to fetch and upload images using HTTP by
upgrading the module dependencies and using the functionality.

Co-author: Brad Fitzpatrick <bradfitz@golang.org>

go.mod

@@ -5,9 +5,6 @@ go 1.12
 require (
 	bazil.org/fuse v0.0.0-20180421153158-65cc252bf669
 	cloud.google.com/go v0.37.2
-	github.com/google/go-containerregistry v0.0.0-20190401170947-eedaddc5e2c8
-	golang.org/x/net v0.0.0-20190320064053-1272bf9dcd53 // indirect
-	golang.org/x/sys v0.0.0-20190321052220-f7bb7a8bee54
-	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
-	gopkg.in/yaml.v2 v2.2.2 // indirect
+	github.com/google/go-containerregistry v0.0.0-20191010200024-a3d713f9b7f8
+	golang.org/x/sys v0.0.0-20190507160741-ecd444e8653b
 )