- cleanup test: we're not installing, so no need to override the user site,
  or skip the test when run with a virtual environment
- use pytest support for capturing output (`context.quiet` does not work
  with Python 2), and check the output

When using Python 2, `python2 -m unittest` is not equivalent to
`python2 -m unittest discover`.

Include license file in the generated wheel package

The wheel package format supports including the license file. This is
done using the [metadata] section in the setup.cfg file. For additional
information on this feature, see:

https://wheel.readthedocs.io/en/stable/index.html#including-the-license-in-the-generated-wheel-file

commands: dist_info: say something!

The dist_info command did not say anything like other
commands did. This gives some more helpful information.

Expect failure on macOS 10.13 and other operating systems where writing latin-1 encoded filenames is prohibited. Fixes #1169.

Tests: Run `python -m pip` instead of plain `pip`

Clean up resource warnings during tests