Properly strip time zones which are west of UTC

[mitya57]

Feature or Bugfix

• Bugfix

Purpose

Properly strip time zones which are west of UTC. Such timezones won’t have + character, they will have - instead.

This fixes test failure which was seen in Debian:

        iso_local = dt.astimezone().isoformat(' ').split('+')[0]
        fd_local = i18n.format_date(fmt, date=dt, language='en', local_time=True)
>       assert fd_local == iso_local
E       AssertionError: assert '2016-08-06 17:11:17' == '2016-08-06 17:11:17-12:00'
E         
E         - 2016-08-06 17:11:17-12:00
E         ?                    ------
E         + 2016-08-06 17:11:17
tests/test_util/test_util_i18n.py:111: AssertionError