Merge component 'engine' from git@github.com:docker/engine 18.09

components/engine/pkg/chrootarchive/chroot_unix.go

@@ -10,3 +10,7 @@ func chroot(path string) error {
 	}
 	return unix.Chdir("/")
 }
+
+func realChroot(path string) error {
+	return chroot(path)
+}