Switch from nose to pytest (#5282)

* 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

setup.cfg

@@ -3,9 +3,3 @@ universal = 1
 
 [easy_install]
 zip_ok = false
-
-[nosetests]
-nocapture=1
-cover-package=certbot,acme,certbot_apache,certbot_nginx
-cover-erase=1
-cover-tests=1