Initial support for getting the leader from Zookeeper.

Some tests included for making sure the JSON blob pulled from Zookeeper
is correct.

Updated client to be able to take Zookeeper json cluster config that is
currently being used in aurora (clusters.json usually located at
/etc/aurora/cluster.json).

Changed error messages to no longer have a period at the end as that was
throwing off printing of the error.

Modified samuel's ZK library slightly to stop verbose logging using a
NoOpLogger from stackoverflow.

vendor/github.com/samuel/go-zookeeper/zk/server_help.go

@@ -0,0 +1,190 @@
+package zk
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"math/rand"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
+type TestServer struct {
+	Port int
+	Path string
+	Srv  *Server
+}
+
+type TestCluster struct {
+	Path    string
+	Servers []TestServer
+}
+
+func StartTestCluster(size int, stdout, stderr io.Writer) (*TestCluster, error) {
+	tmpPath, err := ioutil.TempDir("", "gozk")
+	if err != nil {
+		return nil, err
+	}
+	success := false
+	startPort := int(rand.Int31n(6000) + 10000)
+	cluster := &TestCluster{Path: tmpPath}
+	defer func() {
+		if !success {
+			cluster.Stop()
+		}
+	}()
+	for serverN := 0; serverN < size; serverN++ {
+		srvPath := filepath.Join(tmpPath, fmt.Sprintf("srv%d", serverN))
+		if err := os.Mkdir(srvPath, 0700); err != nil {
+			return nil, err
+		}
+		port := startPort + serverN*3
+		cfg := ServerConfig{
+			ClientPort: port,
+			DataDir:    srvPath,
+		}
+		for i := 0; i < size; i++ {
+			cfg.Servers = append(cfg.Servers, ServerConfigServer{
+				ID:                 i + 1,
+				Host:               "127.0.0.1",
+				PeerPort:           startPort + i*3 + 1,
+				LeaderElectionPort: startPort + i*3 + 2,
+			})
+		}
+		cfgPath := filepath.Join(srvPath, "zoo.cfg")
+		fi, err := os.Create(cfgPath)
+		if err != nil {
+			return nil, err
+		}
+		err = cfg.Marshall(fi)
+		fi.Close()
+		if err != nil {
+			return nil, err
+		}
+
+		fi, err = os.Create(filepath.Join(srvPath, "myid"))
+		if err != nil {
+			return nil, err
+		}
+		_, err = fmt.Fprintf(fi, "%d\n", serverN+1)
+		fi.Close()
+		if err != nil {
+			return nil, err
+		}
+
+		srv := &Server{
+			ConfigPath: cfgPath,
+			Stdout:     stdout,
+			Stderr:     stderr,
+		}
+		if err := srv.Start(); err != nil {
+			return nil, err
+		}
+		cluster.Servers = append(cluster.Servers, TestServer{
+			Path: srvPath,
+			Port: cfg.ClientPort,
+			Srv:  srv,
+		})
+	}
+	if err := cluster.waitForStart(10, time.Second); err != nil {
+		return nil, err
+	}
+	success = true
+	return cluster, nil
+}
+
+func (ts *TestCluster) Connect(idx int) (*Conn, error) {
+	zk, _, err := Connect([]string{fmt.Sprintf("127.0.0.1:%d", ts.Servers[idx].Port)}, time.Second*15)
+	return zk, err
+}
+
+func (ts *TestCluster) ConnectAll() (*Conn, <-chan Event, error) {
+	return ts.ConnectAllTimeout(time.Second * 15)
+}
+
+func (ts *TestCluster) ConnectAllTimeout(sessionTimeout time.Duration) (*Conn, <-chan Event, error) {
+	hosts := make([]string, len(ts.Servers))
+	for i, srv := range ts.Servers {
+		hosts[i] = fmt.Sprintf("127.0.0.1:%d", srv.Port)
+	}
+	zk, ch, err := Connect(hosts, sessionTimeout)
+	return zk, ch, err
+}
+
+func (ts *TestCluster) Stop() error {
+	for _, srv := range ts.Servers {
+		srv.Srv.Stop()
+	}
+	defer os.RemoveAll(ts.Path)
+	return ts.waitForStop(5, time.Second)
+}
+
+// waitForStart blocks until the cluster is up
+func (ts *TestCluster) waitForStart(maxRetry int, interval time.Duration) error {
+	// verify that the servers are up with SRVR
+	serverAddrs := make([]string, len(ts.Servers))
+	for i, s := range ts.Servers {
+		serverAddrs[i] = fmt.Sprintf("127.0.0.1:%d", s.Port)
+	}
+
+	for i := 0; i < maxRetry; i++ {
+		_, ok := FLWSrvr(serverAddrs, time.Second)
+		if ok {
+			return nil
+		}
+		time.Sleep(interval)
+	}
+	return fmt.Errorf("unable to verify health of servers")
+}
+
+// waitForStop blocks until the cluster is down
+func (ts *TestCluster) waitForStop(maxRetry int, interval time.Duration) error {
+	// verify that the servers are up with RUOK
+	serverAddrs := make([]string, len(ts.Servers))
+	for i, s := range ts.Servers {
+		serverAddrs[i] = fmt.Sprintf("127.0.0.1:%d", s.Port)
+	}
+
+	var success bool
+	for i := 0; i < maxRetry && !success; i++ {
+		success = true
+		for _, ok := range FLWRuok(serverAddrs, time.Second) {
+			if ok {
+				success = false
+			}
+		}
+		if !success {
+			time.Sleep(interval)
+		}
+	}
+	if !success {
+		return fmt.Errorf("unable to verify servers are down")
+	}
+	return nil
+}
+
+func (tc *TestCluster) StartServer(server string) {
+	for _, s := range tc.Servers {
+		if strings.HasSuffix(server, fmt.Sprintf(":%d", s.Port)) {
+			s.Srv.Start()
+			return
+		}
+	}
+	panic(fmt.Sprintf("Unknown server: %s", server))
+}
+
+func (tc *TestCluster) StopServer(server string) {
+	for _, s := range tc.Servers {
+		if strings.HasSuffix(server, fmt.Sprintf(":%d", s.Port)) {
+			s.Srv.Stop()
+			return
+		}
+	}
+	panic(fmt.Sprintf("Unknown server: %s", server))
+}