test: skip lj-1470 test for unconfigured timezones

`os.time()` uses `mktime()` to specify time by the given table.
`mktime()` produces the call to `tzset()` to determine the system's
timezone. If the TZ variable does not appear in the environment, the
system timezone is used. The system timezone is configured by copying,
or linking, a file in the tzfile(5) format to /etc/localtime. So, if
this file is omitted (like in RED OS), the errno is set to a non-zero
value. This leads to the nil returned by the `os.time()` for -1 time
value.

This patch skips the test if this file is missed to be sure that we
don't obtain any false positive failures due to system
misconfigurations.

Reviewed-by: Evgeniy Temirgaleev <e.temirgaleev@tarantool.org>
Reviewed-by: Sergey Bronnikov <sergeyb@tarantool.org>
Signed-off-by: Sergey Kaplun <skaplun@tarantool.org>

Author: Buristan

test/tarantool-tests/lj-1470-os-time-epoch-minus-1s.test.lua

@@ -1,9 +1,27 @@
 local tap = require('tap')
 
+local function unconfigured_timezone()
+  -- `os.time()` uses `mktime()` to specify time by the given
+  -- table. `mktime()` produces the call to `tzset()` to determine
+  -- the system's timezone.
+  -- If the TZ variable does not appear in the environment, the
+  -- system timezone is used. The system timezone is configured by
+  -- copying, or linking, a file in the tzfile(5) format to
+  -- /etc/localtime. So, if this file is omitted, the errno is
+  -- set to a non-zero value. This leads to the nil returned by
+  -- the `os.time()` for -1 time value. Let's skip the test if
+  -- this file is missed to be sure that we don't obtain any false
+  -- positive failures due to system misconfigurations.
+  local f = io.open('/etc/localtime', 'r')
+  return not f
+end
+
 -- The test file demonstrates os.time() fail to return -1 time
 -- value.
 -- See also: https://github.com/LuaJIT/LuaJIT/issues/1470.
-local test = tap.test('lj-1470-os-time-epoch-minus-1s')
+local test = tap.test('lj-1470-os-time-epoch-minus-1s'):skipcond({
+  ['Unconfigured timezone rules'] = unconfigured_timezone(),
+})
 
 test:plan(1)