test: flaky replication/gh-3642-misc-* test

On heavy loaded hosts found the following issue:

  [036] --- replication/gh-3642-misc-no-socket-leak-on-replica-disconnect.result	Sun Sep  6 23:49:57 2020
  [036] +++ replication/gh-3642-misc-no-socket-leak-on-replica-disconnect.reject	Mon Sep  7 04:07:06 2020
  [036] @@ -63,7 +63,7 @@
  [036]  ...
  [036]  box.info.replication[1].upstream.status
  [036]  ---
  [036] -- follow
  [036] +- disconnected
  [036]  ...
  [036]  test_run:cmd('switch default')
  [036]  ---

It happened because replication upstream status check occurred too
early, when it was only in 'disconnected' state. To give the
replication status check routine ability to reach the needed 'follow'
state, it need to wait for it using test_run:wait_upstream() routine.

Closes #5276

test/replication/gh-3642-misc-no-socket-leak-on-replica-disconnect.result

@@ -61,9 +61,9 @@ test_run:cmd("setopt delimiter ''");
 ---
 - true
 ...
-box.info.replication[1].upstream.status
+test_run:wait_upstream(1, {status = 'follow'})
 ---
-- follow
+- true
 ...
 test_run:cmd('switch default')
 ---

test/replication/gh-3642-misc-no-socket-leak-on-replica-disconnect.test.lua

@@ -28,7 +28,7 @@ for i = 1, 64 do
 end;
 test_run:cmd("setopt delimiter ''");
 
-box.info.replication[1].upstream.status
+test_run:wait_upstream(1, {status = 'follow'})
 
 test_run:cmd('switch default')