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

tox.ini

@@ -6,9 +6,6 @@
 skipsdist = true
 envlist = modification,py{26,33,34,35,36},cover,lint
 
-# nosetest -v => more verbose output, allows to detect busy waiting
-# loops, especially on Travis
-
 [base]
 # pip installs the requested packages in editable mode
 pip_install = {toxinidir}/tools/pip_install_editable.sh
@@ -96,6 +93,7 @@ deps =
     pyasn1==0.1.9
     pyparsing==1.5.6
     pyrfc3339==1.0
+    pytest==3.2.5
     python-augeas==0.4.1
     pytz==2012c
     requests[security]==2.6.0