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

certbot-nginx/certbot_nginx/tests/configurator_test.py

@@ -24,7 +24,6 @@ from certbot_nginx.tests import util
 class NginxConfiguratorTest(util.NginxTest):
     """Test a semi complex vhost configuration."""
 
-    _multiprocess_can_split_ = True
 
     def setUp(self):
         super(NginxConfiguratorTest, self).setUp()