[PATCH v2 3/5] test: put require in proper places

[Alexander Turenko]

This commit looks good to me.

WBR, Alexander Turenko.

On Fri, Oct 19, 2018 at 07:17:19PM +0300, Sergei Voronezhskii wrote:
> * put `require('fiber')` after each switch server command, because
> sometimes got 'fiber' not defined error
> * use `require('fio')` after `require('test_run').new()`, because
> sometimes got 'fio' not defined error
> 
> Part of #2436, #3232