* 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
* prevent regressions of #5082
* Fix test_leauto_upgrades.sh
test_leauto_upgrades.sh has been incorrectly been succeeding because while peep
doesn't work with newer versions of pip and letsencrypt-auto would crash,
the output included the version number so we reported the test as passing.
This updates letsencrypt-auto to the oldest version that still works for the
purpose of the test and sets pipefail so errors are properly reported.
* Test symlink creation in test_leauto_upgrades.sh
* Pin dependencies in test_sdists.sh.
* Fix permissions errors in test_tests.sh
