Packaging: stop tests distribution as part of package

[penguinolog]

• Make package size smaller
• Tests are useless on client side

Checklist

• I've ensured that similar functionality has not already been implemented
• I've ensured that similar functionality has not earlier been proposed and declined
• I've branched off the master or python-dual-support branch
• I've merged fresh upstream into my branch recently
• I've ran tox successfully in local environment
• I've included docstrings and/or documentation and/or examples for my code (if this is a new feature)

[coveralls]

coverage: 77.255% (+3.7%) from 73.566% when pulling 694e89a on penguinolog:packaging_tests into 7ab8347 on urwid:master.