Add support for make vendor-in-container

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

vendor/github.com/ulikunitz/xz/example.go

@@ -1,40 +0,0 @@
-// Copyright 2014-2017 Ulrich Kunitz. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build ignore
-
-package main
-
-import (
-	"bytes"
-	"io"
-	"log"
-	"os"
-
-	"github.com/ulikunitz/xz"
-)
-
-func main() {
-	const text = "The quick brown fox jumps over the lazy dog.\n"
-	var buf bytes.Buffer
-	// compress text
-	w, err := xz.NewWriter(&buf)
-	if err != nil {
-		log.Fatalf("xz.NewWriter error %s", err)
-	}
-	if _, err := io.WriteString(w, text); err != nil {
-		log.Fatalf("WriteString error %s", err)
-	}
-	if err := w.Close(); err != nil {
-		log.Fatalf("w.Close error %s", err)
-	}
-	// decompress buffer and write output to stdout
-	r, err := xz.NewReader(&buf)
-	if err != nil {
-		log.Fatalf("NewReader error %s", err)
-	}
-	if _, err = io.Copy(os.Stdout, r); err != nil {
-		log.Fatalf("io.Copy error %s", err)
-	}
-}