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

tools/release.sh

@@ -55,7 +55,7 @@ SUBPKGS="$SUBPKGS_IN_AUTO $SUBPKGS_NOT_IN_AUTO"
 subpkgs_modules="$(echo $SUBPKGS | sed s/-/_/g)"
 # certbot_compatibility_test is not packaged because:
 # - it is not meant to be used by anyone else than Certbot devs
-# - it causes problems when running nosetests - the latter tries to
+# - it causes problems when running pytest - the latter tries to
 #   run everything that matches test*, while there are no unittests
 #   there
 
@@ -166,10 +166,10 @@ fi
 mkdir kgs
 kgs="kgs/$version"
 pip freeze | tee $kgs
-pip install nose
+pip install pytest
 for module in $subpkgs_modules ; do
     echo testing $module
-    nosetests $module
+    pytest --pyargs $module
 done
 cd ~-