[PATCH] test: fix app/fiber.test.lua flaky fails

[Vladimir Davydov]

On Sun, Dec 02, 2018 at 08:05:07PM +0300, Alexander Turenko wrote:
> Fixes #3852.
> ---
> 
> https://github.com/tarantool/tarantool/issues/3852
> https://github.com/tarantool/tarantool/tree/Totktonada/gh-3852-fix-flaky-app-fiber-test-lua
> 
> The branch is based on top of 2.1. Please, cherry-pick the fix to 1.10
> too.

Pushed to 2.1 and 1.10.