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/docker/docker-credential-helpers/client/command.go

@@ -1,56 +0,0 @@
-package client
-
-import (
-	"fmt"
-	"io"
-	"os"
-	"os/exec"
-)
-
-// Program is an interface to execute external programs.
-type Program interface {
-	Output() ([]byte, error)
-	Input(in io.Reader)
-}
-
-// ProgramFunc is a type of function that initializes programs based on arguments.
-type ProgramFunc func(args ...string) Program
-
-// NewShellProgramFunc creates programs that are executed in a Shell.
-func NewShellProgramFunc(name string) ProgramFunc {
-	return NewShellProgramFuncWithEnv(name, nil)
-}
-
-// NewShellProgramFuncWithEnv creates programs that are executed in a Shell with environment variables
-func NewShellProgramFuncWithEnv(name string, env *map[string]string) ProgramFunc {
-	return func(args ...string) Program {
-		return &Shell{cmd: createProgramCmdRedirectErr(name, args, env)}
-	}
-}
-
-func createProgramCmdRedirectErr(commandName string, args []string, env *map[string]string) *exec.Cmd {
-	programCmd := exec.Command(commandName, args...)
-	programCmd.Env = os.Environ()
-	if env != nil {
-		for k, v := range *env {
-			programCmd.Env = append(programCmd.Env, fmt.Sprintf("%s=%s", k, v))
-		}
-	}
-	programCmd.Stderr = os.Stderr
-	return programCmd
-}
-
-// Shell invokes shell commands to talk with a remote credentials helper.
-type Shell struct {
-	cmd *exec.Cmd
-}
-
-// Output returns responses from the remote credentials helper.
-func (s *Shell) Output() ([]byte, error) {
-	return s.cmd.Output()
-}
-
-// Input sets the input to send to a remote credentials helper.
-func (s *Shell) Input(in io.Reader) {
-	s.cmd.Stdin = in
-}