test: tarantoolctl: verify delayed box.cfg()

app-tap.tarantoolctl.test.lua fails after
17df9edf ('tarantoolctl: allow to start
instances with delayed box.cfg{}').

The commit fixes the test case that did check that an error is reported
if box.cfg() was not called in an instance script.

Follows up #4435.
Fixes #4448.

(cherry picked from commit 6c627af3)

test/app-tap/tarantoolctl.test.lua

@@ -179,13 +179,18 @@ test:plan(8)
 do
     local dir = fio.tempdir()
     create_script(dir, 'script.lua', [[ box.cfg{memtx_memory = 104857600} ]])
-    create_script(dir, 'no_box_cfg.lua', [[ print('Hi!') ]])
+    create_script(dir, 'delayed_box_cfg.lua', [[
+        local fiber = require('fiber')
+        fiber.create(function()
+            fiber.sleep(1)
+            box.cfg{}
+        end)
+    ]])
 
     local status, err = pcall(function()
         test:test("basic test", function(test_i)
             test_i:plan(18)
-            check_ok(test_i, dir, 'start', 'no_box_cfg', 1, nil, "Starting instance",
-                     "box.cfg() is not called in an instance file")
+            check_ok(test_i, dir, 'start', 'delayed_box_cfg', 0, nil, "Starting instance")
             check_ok(test_i, dir, 'start',  'script', 0, nil, "Starting instance")
             tctl_wait_start(dir, 'script')
             check_ok(test_i, dir, 'status', 'script', 0, nil, "is running")