box: replication shouldn't leak user password

It was possible to leak user password through setting 'replication'
configuration option in first box.cfg invocation. This happened due
to unconditional logging in load_cfg function. The patch introduces
conditional logging.

Closes #4493

src/box/lua/load_cfg.lua

@@ -564,6 +564,9 @@ local function load_cfg(cfg)
                 fun()
             end
             if not compare_cfg(val, default_cfg[key]) then
+                if log_cfg_option[key] ~= nil then
+                    val = log_cfg_option[key](val)
+                end
                 log.info("set '%s' configuration option to %s", key, json.encode(val))
             end
         end

test/box/cfg.result

@@ -591,3 +591,33 @@ test_run:cmd("cleanup server cfg_tester6")
  | ---
  | - true
  | ...
+
+--
+-- gh-4493: Replication user password may leak to logs
+--
+test_run:cmd('create server cfg_tester7 with script = "box/lua/cfg_test6.lua"')
+ | ---
+ | - true
+ | ...
+test_run:cmd("start server cfg_tester7")
+ | ---
+ | - true
+ | ...
+-- test there is replication log in log
+test_run:grep_log('cfg_tester7', 'set \'replication\' configuration option to', 1000)
+ | ---
+ | - set 'replication' configuration option to
+ | ...
+-- test there is no password in log
+test_run:grep_log('cfg_tester7', 'test%-cluster%-cookie', 1000)
+ | ---
+ | - null
+ | ...
+test_run:cmd("stop server cfg_tester7")
+ | ---
+ | - true
+ | ...
+test_run:cmd("cleanup server cfg_tester7")
+ | ---
+ | - true
+ | ...

test/box/cfg.test.lua

@@ -142,3 +142,15 @@ test_run:cmd("start server cfg_tester6")
 test_run:grep_log('cfg_tester6', 'set \'vinyl_memory\' configuration option to 1073741824', 1000)
 test_run:cmd("stop server cfg_tester6")
 test_run:cmd("cleanup server cfg_tester6")
+
+--
+-- gh-4493: Replication user password may leak to logs
+--
+test_run:cmd('create server cfg_tester7 with script = "box/lua/cfg_test6.lua"')
+test_run:cmd("start server cfg_tester7")
+-- test there is replication log in log
+test_run:grep_log('cfg_tester7', 'set \'replication\' configuration option to', 1000)
+-- test there is no password in log
+test_run:grep_log('cfg_tester7', 'test%-cluster%-cookie', 1000)
+test_run:cmd("stop server cfg_tester7")
+test_run:cmd("cleanup server cfg_tester7")

test/box/lua/cfg_test6.lua

+#!/usr/bin/env tarantool
+os = require('os')
+
+box.cfg{
+    listen = os.getenv("LISTEN"),
+    replication         = "admin:test-cluster-cookie@" .. os.getenv("LISTEN"),
+    replication_connect_timeout = 0.1,
+}
+
+require('console').listen(os.getenv('ADMIN'))