[Checkins] [zopefoundation/zope.interface] 271106: Clean up appveyor.yml

[Marius Gedminas]

  Branch: refs/heads/appveyor-cleanup
  Home:   https://github.com/zopefoundation/zope.interface
  Commit: 271106a02c22e7905b5652070a8c4c19eb8424f8
      https://github.com/zopefoundation/zope.interface/commit/271106a02c22e7905b5652070a8c4c19eb8424f8
  Author: Marius Gedminas <marius at gedmin.as>
  Date:   2019-11-11 (Mon, 11 Nov 2019)

  Changed paths:
    M appveyor.yml

  Log Message:
  -----------
  Clean up appveyor.yml

- Make sure that the Python we want actually exists (and install it if
  necessary) -- this will make our lives easier next year, when Python
  3.9 shows up

- Make the test run quiet (setup.py test -q ignores the -q)

- Pass --skip-existing to twine upload so the build of the tag can be
  retried if necessary without causing spurious failures

I think it might also be a good idea to add a custom version template to
avoid nonsense like https://ci.appveyor.com/project/mgedmin/zope-interface/builds/28770734,
but I'm not entirely sure what happened there and whether a custom
version template would help.  (All I know is all my project appveyors
YML have `version: build-{build}-{branch}` and I've never seen that kind
of error.)