use ssl.create_default_context and SNI if available

Build meta: fixes and cleanups

Fix test command

support `setup_requires` in setup.cfg

python 3 bdist_egg --exclude-source-files __pycache__ issue

- 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`.