Stop testing with py2

Python 2 is no longer supported. Python 3 is required.
This patch stops testing with Python 2 and issues the release note.

Change-Id: I7dc416927ea23d581dbee366d54a733ee53498cf

.zuul.yaml

@@ -2,6 +2,5 @@
     templates:
       - check-requirements
       - openstack-lower-constraints-jobs
-      - openstack-python-jobs
       - openstack-python3-ussuri-jobs
       - release-notes-jobs-python3

doc/requirements.txt

@@ -3,5 +3,4 @@
 # process, which may cause wedges in the gate later.
 openstackdocstheme>=1.18.1 # Apache-2.0
 reno>=2.5.0 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7'  # BSD
 sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4'  # BSD

releasenotes/notes/drop-python2-c3c1601e92a9b87a.yaml

@@ -0,0 +1,4 @@
+---
+upgrade:
+  - |
+    Python 2 is no longer supported. Python 3 is required.

setup.cfg

@@ -5,8 +5,6 @@ description-file = README.rst
 license = Apache Software License
 classifiers =
     Programming Language :: Python
-    Programming Language :: Python :: 2
-    Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7

tox.ini

@@ -1,8 +1,10 @@
 [tox]
-minversion = 2.0
+minversion = 3.1.1
-envlist = py27,py36,py37,pep8
+envlist = py36,py37,pep8
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 install_command = pip install {opts} {packages}
 deps =
        -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
@@ -14,7 +16,6 @@ commands =
     python setup.py testr --slowest --testr-args="{posargs}"
 
 [testenv:pep8]
-basepython = python3
 commands = flake8
 
 [flake8]
@@ -28,7 +29,6 @@ exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg
 import_exceptions = blazarclient.i18n
 
 [testenv:venv]
-basepython = python3
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
   -r{toxinidir}/requirements.txt
@@ -36,19 +36,16 @@ deps =
 commands = {posargs}
 
 [testenv:cover]
-basepython = python3
 commands =
   python setup.py testr --coverage --testr-args='{posargs}'
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt
   -r{toxinidir}/requirements.txt
 
 [testenv:releasenotes]
-basepython = python3
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
   -r{toxinidir}/requirements.txt