Add version label to the cluster. (#96)

* Add version label to the cluster.

According to the STUPS team the daemon that exports logs to scalyr
stops the export if the version label is missing.

* Move label names to constants. 

* Run go fmt

pkg/util/util.go

@@ -5,13 +5,14 @@ import (
 	"encoding/hex"
 	"fmt"
 	"math/rand"
+	"strings"
 	"time"
 
 	"github.com/motomux/pretty"
+	"k8s.io/client-go/pkg/api/v1"
 
 	"github.bus.zalan.do/acid/postgres-operator/pkg/spec"
-	"k8s.io/client-go/pkg/api/v1"
-	"strings"
+	"github.bus.zalan.do/acid/postgres-operator/pkg/util/constants"
 )
 
 var passwordChars = []byte("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")
@@ -37,7 +38,7 @@ func NameFromMeta(meta v1.ObjectMeta) spec.NamespacedName {
 }
 
 func PodClusterName(pod *v1.Pod) spec.NamespacedName {
-	if name, ok := pod.Labels["spilo-cluster"]; ok {
+	if name, ok := pod.Labels[constants.ClusterNameLabel]; ok {
 		return spec.NamespacedName{
 			Namespace: pod.Namespace,
 			Name:      name,
@@ -48,7 +49,7 @@ func PodClusterName(pod *v1.Pod) spec.NamespacedName {
 }
 
 func PodSpiloRole(pod *v1.Pod) string {
-	return pod.Labels["spilo-role"]
+	return pod.Labels[constants.SpiloRoleLabel]
 }
 
 func PGUserPassword(user spec.PgUser) string {