e2e: add basic release migration test

For #5697.

```
MIGRATION_FROM=v3.0.2 go test -v -run TestReleaseMigrate
```

e2e/ctl_v3_migrate_test.go

@@ -52,7 +52,7 @@ func TestCtlV3Migrate(t *testing.T) {
 	for i := range epc.procs {
 		dataDirs[i] = epc.procs[i].cfg.dataDirPath
 	}
-	if err := epc.Stop(); err != nil {
+	if err := epc.StopAll(); err != nil {
 		t.Fatalf("error closing etcd processes (%v)", err)
 	}
 
@@ -74,7 +74,7 @@ func TestCtlV3Migrate(t *testing.T) {
 	for i := range epc.procs {
 		epc.procs[i].cfg.keepDataDir = true
 	}
-	if err := epc.Restart(); err != nil {
+	if err := epc.RestartAll(); err != nil {
 		t.Fatal(err)
 	}
 

e2e/etcd_release_migrate_test.go

@@ -0,0 +1,81 @@
+package e2e
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/coreos/etcd/pkg/testutil"
+)
+
+// TestReleaseMigrate ensures that changes to master branch does not affect the
+// migration from latest etcd releases.
+func TestReleaseMigrate(t *testing.T) {
+	ver := os.Getenv("MIGRATION_FROM")
+	if ver == "" {
+		t.Skipf("skipping release migration tests (version %q)", ver)
+	}
+
+	const (
+		fileNameTmpl     = "etcd-{{.Version}}-linux-amd64.tar.gz"
+		extractedDirTmpl = "etcd-{{.Version}}-linux-amd64"
+		googleTmpl       = "https://storage.googleapis.com/etcd/{{.Version}}/etcd-{{.Version}}-linux-amd64.tar.gz"
+		githubTmpl       = "https://github.com/coreos/etcd/releases/download/{{.Version}}/etcd-{{.Version}}-linux-amd64.tar.gz"
+	)
+	var (
+		fileName          = insertVersion(fileNameTmpl, ver)
+		extractedDir      = insertVersion(extractedDirTmpl, ver)
+		releaseBinaryPath = filepath.Join(extractedDir, "etcd")
+	)
+	os.RemoveAll(fileName)
+	os.RemoveAll(extractedDir)
+	if err := downloadExtract(fileName, insertVersion(googleTmpl, ver), insertVersion(githubTmpl, ver)); err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		os.RemoveAll(fileName)
+		os.RemoveAll(extractedDir)
+	}()
+
+	defer testutil.AfterTest(t)
+
+	copiedCfg := configNoTLS
+	copiedCfg.execPath = releaseBinaryPath
+	epc, err := newEtcdProcessCluster(&copiedCfg)
+	if err != nil {
+		t.Fatalf("could not start etcd process cluster (%v)", err)
+	}
+	defer func() {
+		if errC := epc.Close(); errC != nil {
+			t.Fatalf("error closing etcd processes (%v)", errC)
+		}
+	}()
+
+	os.Setenv("ETCDCTL_API", "3")
+	defer os.Unsetenv("ETCDCTL_API")
+	cx := ctlCtx{
+		t:           t,
+		cfg:         configNoTLS,
+		dialTimeout: 7 * time.Second,
+		quorum:      true,
+		epc:         epc,
+	}
+	if err := ctlV3Put(cx, "foo", "bar", ""); err != nil {
+		cx.t.Fatalf("ctlV3Put error (%v)", err)
+	}
+
+	for i := range epc.backends() {
+		if err := epc.Stop(i); err != nil {
+			t.Fatalf("error closing etcd process (%v)", err)
+		}
+		epc.procs[i].cfg.execPath = "../bin/etcd"
+		epc.procs[i].cfg.keepDataDir = true
+		if err := epc.Restart(i); err != nil {
+			t.Fatalf("error restarting etcd process (%v)", err)
+		}
+		if err := ctlV3Get(cx, []string{"foo"}, []kv{{"foo", "bar"}}...); err != nil {
+			cx.t.Fatalf("ctlV3Get error (%v)", err)
+		}
+	}
+}

e2e/etcd_release_migrate_util.go

@@ -0,0 +1,131 @@
+// Copyright 2016 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package e2e
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"fmt"
+	"html/template"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"runtime"
+)
+
+func downloadExtract(fileName string, urls ...string) error {
+	f, err := os.Create(fileName)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	for _, url := range urls {
+		var resp *http.Response
+		resp, err = http.Get(url)
+		if err != nil {
+			continue
+		}
+		defer resp.Body.Close()
+
+		_, err = io.Copy(f, resp.Body)
+		if err != nil {
+			continue
+		}
+		break
+	}
+	if err != nil {
+		return err
+	}
+	return extractTarGz(fileName)
+}
+
+func insertVersion(tmpl, ver string) string {
+	buf := new(bytes.Buffer)
+	if err := template.Must(template.New("tmpl").Parse(tmpl)).Execute(buf, struct{ Version string }{ver}); err != nil {
+		panic(err)
+	}
+	return buf.String()
+}
+
+func extractTarGz(target string) error {
+	f, err := os.Open(target)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	gr, err := gzip.NewReader(f)
+	if err != nil {
+		return err
+	}
+	defer gr.Close()
+
+	tr := tar.NewReader(gr)
+	for {
+		header, err := tr.Next()
+		if err == io.EOF {
+			break
+		} else if err != nil {
+			return err
+		}
+
+		if err := untar(tr, header); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func untar(tr *tar.Reader, header *tar.Header) error {
+	switch header.Typeflag {
+	case tar.TypeDir:
+		return os.MkdirAll(header.Name, 0700)
+	case tar.TypeReg, tar.TypeRegA:
+		return writeFile(header.Name, tr, header.FileInfo().Mode())
+	case tar.TypeSymlink:
+		return writeSymlink(header.Name, header.Linkname)
+	default:
+		return fmt.Errorf("%s has unknown type %v", header.Name, header.Typeflag)
+	}
+}
+
+func writeFile(fpath string, rd io.Reader, mode os.FileMode) error {
+	if err := os.MkdirAll(filepath.Dir(fpath), 0700); err != nil {
+		return err
+	}
+
+	f, err := os.Create(fpath)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	if err = f.Chmod(mode); err != nil && runtime.GOOS != "windows" {
+		return err
+	}
+
+	_, err = io.Copy(f, rd)
+	return err
+}
+
+func writeSymlink(fpath string, target string) error {
+	if err := os.MkdirAll(filepath.Dir(fpath), 0700); err != nil {
+		return err
+	}
+	return os.Symlink(target, fpath)
+}