Switch from containers/image to go-containerregistry (#140)

* Vendor changes for go-containerregistry switch.

* Manual changes for go-containerregistry switch.

The biggest change is refactoring the tarball unpacking.

* Pull more of container-diff out.

* More vendor removals.

* More unit tests.

vendor/github.com/Microsoft/hcsshim/processimage.go

@@ -1,23 +0,0 @@
-package hcsshim
-
-import "os"
-
-// ProcessBaseLayer post-processes a base layer that has had its files extracted.
-// The files should have been extracted to <path>\Files.
-func ProcessBaseLayer(path string) error {
-	err := processBaseImage(path)
-	if err != nil {
-		return &os.PathError{Op: "ProcessBaseLayer", Path: path, Err: err}
-	}
-	return nil
-}
-
-// ProcessUtilityVMImage post-processes a utility VM image that has had its files extracted.
-// The files should have been extracted to <path>\Files.
-func ProcessUtilityVMImage(path string) error {
-	err := processUtilityImage(path)
-	if err != nil {
-		return &os.PathError{Op: "ProcessUtilityVMImage", Path: path, Err: err}
-	}
-	return nil
-}