Bug in rfc3339 implementation

[ofek]

This issue can be easily reproduced like so (same on Python 2.7.15):

$ python
Python 3.7.2 (default, Feb 21 2019, 17:35:59) [MSC v.1915 64 bit (AMD64)] :: Anaconda, Inc. on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from datetime import datetime, timedelta
>>> from time import sleep
>>> from kubernetes.config.dateutil import UTC, format_rfc3339, parse_rfc3339
>>>
>>> for tz in (None, UTC):
...     dt = parse_rfc3339(datetime.now(tz) + timedelta(seconds=20))
...     sleep(0.5)
...     delta = dt - datetime.now(dt.tzinfo)
...     print('Delta of {} should be ~19.5, and was {}'.format(format_rfc3339(dt), delta.total_seconds()))
...
Delta of 2019-03-18T00:21:17Z should be ~19.5, and was -14380.501032
Delta of 2019-03-18T04:21:17Z should be ~19.5, and was 19.499945

Based on this comment, there is logic that is supposed to coerce naive date times to UTC but it does not appear to be working consistently cc @mbohlool @pokoli

I should also note, this exact example passes on Travis (Xenial):

Job: https://travis-ci.com/DataDog/integrations-core/jobs/185296386#L592
Test: https://github.com/DataDog/integrations-core/blob/e3b1d64dfb1f40ec8e0b311752960ebd488387dd/datadog_checks_base/tests/test_kube_leader.py#L162-L168
Code: https://github.com/DataDog/integrations-core/blob/e3b1d64dfb1f40ec8e0b311752960ebd488387dd/datadog_checks_base/datadog_checks/base/checks/kube_leader/record.py#L75-L83

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[k8s-ci-robot]

@fejta-bot: Closing this issue.

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