builder/amazonebs: check for err parsing template for ami name

builder/amazonebs/step_create_ami.go

@@ -29,7 +29,11 @@ func (s *stepCreateAMI) Run(state map[string]interface{}) multistep.StepAction {
 		strconv.FormatInt(time.Now().UTC().Unix(), 10),
 	}
 
-	t := template.Must(template.New("ami").Parse(config.AMIName))
+	t, err := template.New("ami").Parse(config.AMIName)
+	if err != nil {
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
 	t.Execute(amiNameBuf, tData)
 	amiName := amiNameBuf.String()