devel/py-pytest: Update to 3.6.2

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Summary

Proposed commit log message:

devel/py-pytest: Update to 3.6.2

Changes:
  https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst

- Update PORTVERSION and distinfo checksum to 3.6.2
- Add devel/py-more-itertools [0] and devel/py-atomicwrites [1] to RUN_DEPENDS
- Add shells/bash [2] to TEST_DEPENDS
- Change test target to run pytest, setup.py test has been removed [3]

[0] https://github.com/pytest-dev/pytest/commit/25399da9047d044174f090f1315f9a4244b91135
[1] https://github.com/pytest-dev/pytest/commit/aa95a425d7708d80fc887b1825662daf3a624ba7
[2] https://github.com/pytest-dev/pytest/blob/master/testing/test_argcomplete.py
[3] https://github.com/pytest-dev/pytest/commit/c1d9ca81df5364417317fd779e73d9ff85fe5d35

Reviewed_by: koobs
Approved by: koobs (mentor)
Differential_Revision: D16124

Test Plan

• portlint: OK (looks fine.)
• testport: OK (poudriere: 1200069, [armv7, aarch64], '', [py27, py36] tested)
• unittest: OK (

Python2.7 on aarch64: 3 failed, 2048 passed, 36 skipped, 36 xfailed, 2 warnings
Python3.6 on aarch64: 3 failed, 2052 passed, 32 skipped, 36 xfailed, 3 warnings
)

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Thanks @koobs.