new package: compression (ported from docker/pkg/archive)

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

vendor/github.com/opencontainers/runc/libcontainer/user/lookup_unix.go

@@ -1,30 +0,0 @@
-// +build darwin dragonfly freebsd linux netbsd openbsd solaris
-
-package user
-
-import (
-	"io"
-	"os"
-)
-
-// Unix-specific path to the passwd and group formatted files.
-const (
-	unixPasswdPath = "/etc/passwd"
-	unixGroupPath  = "/etc/group"
-)
-
-func GetPasswdPath() (string, error) {
-	return unixPasswdPath, nil
-}
-
-func GetPasswd() (io.ReadCloser, error) {
-	return os.Open(unixPasswdPath)
-}
-
-func GetGroupPath() (string, error) {
-	return unixGroupPath, nil
-}
-
-func GetGroup() (io.ReadCloser, error) {
-	return os.Open(unixGroupPath)
-}