Update py-test to 2.8.6:

2.8.6
-----

- fix #1259: allow for double nodeids in junitxml,
  this was a regression failing plugins combinations
  like pytest-pep8 + pytest-flakes

- Workaround for exception that occurs in pyreadline when using
  ``--pdb`` with standard I/O capture enabled.
  Thanks Erik M. Bray for the PR.

- fix #900: Better error message in case the target of a ``monkeypatch`` call
  raises an ``ImportError``.

- fix #1292: monkeypatch calls (setattr, setenv, etc.) are now O(1).
  Thanks David R. MacIver for the report and Bruno Oliveira for the PR.

- fix #1223: captured stdout and stderr are now properly displayed before
  entering pdb when ``--pdb`` is used instead of being thrown away.
  Thanks Cal Leeming for the PR.

- fix #1305: pytest warnings emitted during ``pytest_terminal_summary`` are now
  properly displayed.
  Thanks Ionel Maries Cristian for the report and Bruno Oliveira for the PR.

- fix #628: fixed internal UnicodeDecodeError when doctests contain unicode.
  Thanks Jason R. Coombs for the report and Bruno Oliveira for the PR.

- fix #1334: Add captured stdout to jUnit XML report on setup error.
  Thanks Georgy Dyuldin for the PR.

2.8.5
-----

- fix #1243: fixed issue where class attributes injected during collection could break pytest.
  PR by Alexei Kozlenok, thanks Ronny Pfannschmidt and Bruno Oliveira for the review and help.

- fix #1074: precompute junitxml chunks instead of storing the whole tree in objects
  Thanks Bruno Oliveira for the report and Ronny Pfannschmidt for the PR

- fix #1238: fix ``pytest.deprecated_call()`` receiving multiple arguments
  (Regression introduced in 2.8.4). Thanks Alex Gaynor for the report and
  Bruno Oliveira for the PR.

2.8.4
-----

- fix #1190: ``deprecated_call()`` now works when the deprecated
  function has been already called by another test in the same
  module. Thanks Mikhail Chernykh for the report and Bruno Oliveira for the
  PR.

- fix #1198: ``--pastebin`` option now works on Python 3. Thanks
  Mehdy Khoshnoody for the PR.

- fix #1219: ``--pastebin`` now works correctly when captured output contains
  non-ascii characters. Thanks Bruno Oliveira for the PR.

- fix #1204: another error when collecting with a nasty __getattr__().
  Thanks Florian Bruhin for the PR.

- fix the summary printed when no tests did run.
  Thanks Florian Bruhin for the PR.
- fix #1185 - ensure MANIFEST.in exactly matches what should go to a sdist

- a number of documentation modernizations wrt good practices.
  Thanks Bruno Oliveira for the PR.

(wiz)