test: put require in proper places

* 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

test/replication/catch.test.lua

@@ -2,7 +2,6 @@ env = require('test_run')
 test_run = env.new()
 engine = test_run:get_cfg('engine')
 
-
 net_box = require('net.box')
 errinj = box.error.injection
 

test/replication/gc.result

-fio = require 'fio'
----
-...
 test_run = require('test_run').new()
 ---
 ...
@@ -13,6 +10,9 @@ replica_set = require('fast_replica')
 fiber = require('fiber')
 ---
 ...
+fio = require('fio')
+---
+...
 test_run:cleanup_cluster()
 ---
 ...

test/replication/gc.test.lua

-fio = require 'fio'
 test_run = require('test_run').new()
 engine = test_run:get_cfg('engine')
 replica_set = require('fast_replica')
 fiber = require('fiber')
+fio = require('fio')
 
 test_run:cleanup_cluster()
 test_run:cmd("create server replica with rpl_master=default, script='replication/replica.lua'")

test/replication/on_replace.result

@@ -63,6 +63,9 @@ test_run:cmd("switch replica")
 ---
 - true
 ...
+fiber = require('fiber')
+---
+...
 while box.space.test:count() < 2 do fiber.sleep(0.01) end
 ---
 ...

test/replication/on_replace.test.lua

@@ -26,6 +26,7 @@ session_type
 test_run:cmd("switch default")
 box.space.test:insert{2}
 test_run:cmd("switch replica")
+fiber = require('fiber')
 while box.space.test:count() < 2 do fiber.sleep(0.01) end
 --
 -- applier