title: tarantool queue attempt to index global 'queue'
body: <ol>
  <li><p>I have error in line: 
  <code>que := queue.New(conn, "foobar")</code>
  : Error eval:1: attempt to index global 'queue' (a nil value) (0x20)</p></li>
  <li><p>Config file: (if i delete box.once then erros tube is exists)
  How to correct init users and tube in config, without error 'user already exist`?</p></li>
  </ol>
  
  <p>`</p>
  
  <pre><code>box.cfg {listen=3303}
  local queue = require('queue')
  queue.start()
  queue.create_tube('foobar', 'fifottl', {if_not_exists=true})
  box.once("init", function()
      box.schema.user.grant('guest', 'read,write,execute', 'universe')
  end)
  </code></pre>
  
  <p>`</p>
  
  <p>code:
  `</p>
  
  <pre><code>func TestTarantoolQueue(t *testing.T)  {
      //opts := tarantool.Opts{User: "test", Pass: "test"}
      opts := tarantool.Opts{}
      conn, err := tarantool.Connect("127.0.0.1:3303", opts)
      if err != nil {
          t.Log("Error", err)
          t.FailNow()
      }
      cfg := queue.Cfg{
          Temporary: true,
          IfNotExists: true,
          Kind: queue.FIFO_TTL,
          Opts: queue.Opts{
              Ttl: 10 * time.Second,
              Ttr: 5 * time.Second,
              Delay: 3 * time.Second,
              Pri: 1,
          },
      }
      que := queue.New(conn, "foobar")
      err = que.Create(cfg)
      if err != nil {
          t.Log("Error", err)
          t.FailNow()
      }
      task, err := que.Put("test_data")
      if err != nil {
          t.Log("Error", err)
          t.FailNow()
      }
      fmt.Println("Task id is ", task.Id())
      task, err = que.Take() //blocking operation
      if err != nil {
          t.Log("Error", err)
          t.FailNow()
      }
      fmt.Println("Data is ", task.Data())
      task.Ack()
      task, err = que.Put([]int{1, 2, 3})
      if err != nil {
          t.Log("Error", err)
          t.FailNow()
      }
      task.Bury()
      task, err = que.TakeTimeout(2 * time.Second)
      if task == nil {
          fmt.Println("Task is nil")
      }
      que.Drop()
  }
  </code></pre>
  
  <p>`</p>