kubeadm: print the stack trace of an error for klog level v>=5

- replace all stray calls of os.Exit() to util.CheckError() instead
- CheckError() now checks if the klog verbosity level is >=5
and shows a stack trace of the error
- don't call klog.Fatal in version.go

cmd/kubeadm/kubeadm.go

@@ -17,13 +17,10 @@ limitations under the License.
 package main
 
 import (
-	"os"
-
 	"k8s.io/kubernetes/cmd/kubeadm/app"
+	"k8s.io/kubernetes/cmd/kubeadm/app/util"
 )
 
 func main() {
-	if err := app.Run(); err != nil {
-		os.Exit(1)
-	}
+	util.CheckErr(app.Run())
 }