In addition to the speed improvements in CI, the speed improvements locally with both this https://github.com/certbot/certbot/pull/9666 which this builds on is even more significant. After it's been run once so it's had a chance to set up the different virtual environments, `tox` locally now takes 39 seconds on my laptop when it used to take 137 seconds.
* Get integration tests working on python 3.8
* Run unit tests on py38
* Update coveragercs to use coverage 4.5+ format
* remove line added to tox.ini
* update changelog
* xenial is the new travis default; no need to specify in .travis.yml
* Use pipstrap to install a good version of pip
* Use pytest in cb-auto tests
* Remove nose usage in auto_test.py
* remove nose dev dep
* use pytest in test_tests
* Use pytest in tox
* Update dev dependency pinnings
* remove nose multiprocess lines
* Use pytest for coverage
* Use older py and pytest for old python versions
* Add test for Error.__str__
* pin pytest in oldest test
* Fix tests for DNS-DO plugin on py26
* Work around bug for Python 3.3
* Clarify dockerfile comments
