test: flaky replication/replica_rejoin.test.lua

On heavy loaded hosts found the following issue:

  [151] --- replication/replica_rejoin.result     Tue Sep 29 10:57:26 2020
  [151] +++ replication/replica_rejoin.reject     Tue Sep 29 10:57:48 2020
  [151] @@ -230,7 +230,12 @@
  [151]      return box.info ~= nil and box.info.replication[1] ~= nil
  [151]  end)
  [151]  ---
  [151] -- true
  [151] +- error: "builtin/box/load_cfg.lua:601: Please call box.cfg{} first\nstack traceback:\n\tbuiltin/box/load_cfg.lua:601:
  [151] +    in function '__index'\n\t[string \"return test_run:wait_cond(function()         ...\"]:1:
  [151] +    in function 'cond'\n\t/tmp/tnt/151_replication/test_run.lua:411: in function </tmp/tnt/151_replication/test_run.lua:404>\n\t[C]:
  [151] +    in function 'pcall'\n\tbuiltin/box/console.lua:402: in function 'eval'\n\tbuiltin/box/console.lua:708:
  [151] +    in function 'repl'\n\tbuiltin/box/console.lua:842: in function <builtin/box/console.lua:828>\n\t[C]:
  [151] +    in function 'pcall'\n\tbuiltin/socket.lua:1081: in function <builtin/socket.lua:1079>"
  [151]  ...
  [151]  test_run:wait_upstream(1, {message_re = 'Missing %.xlog file', status = 'loading'})
  [151]  ---
  [151]

It happened because box.cfg was not ready to provide information. In
real there is no need to use local check for replication information
parts availablity, due to wait_upstream() function used below, do it
itself.

Part of #4985

test/replication/replica_rejoin.result

@@ -224,14 +224,6 @@ test_run:cmd("switch replica")
 ---
 - true
 ...
--- Need to wait for box.info.replication[1] defined, otherwise test-run fails to
--- wait for the upstream status sometimes.
-test_run:wait_cond(function()                                                   \
-    return box.info ~= nil and box.info.replication[1] ~= nil                   \
-end)
----
-- true
-...
 test_run:wait_upstream(1, {message_re = 'Missing %.xlog file', status = 'loading'})
 ---
 - true

test/replication/replica_rejoin.test.lua

@@ -82,11 +82,6 @@ test_run:wait_cond(function() return #fio.glob(fio.pathjoin(box.cfg.wal_dir, '*.
 box.cfg{checkpoint_count = checkpoint_count}
 test_run:cmd("start server replica with args='true', wait=False")
 test_run:cmd("switch replica")
--- Need to wait for box.info.replication[1] defined, otherwise test-run fails to
--- wait for the upstream status sometimes.
-test_run:wait_cond(function()                                                   \
-    return box.info ~= nil and box.info.replication[1] ~= nil                   \
-end)
 test_run:wait_upstream(1, {message_re = 'Missing %.xlog file', status = 'loading'})
 box.space.test:select()