[ussuri][goal] Drop python 2.7 support and testing

OpenStack is dropping the py2.7 support in ussuri cycle.

bashate is ready with python 3 and ok to drop the
python 2.7 support.

Complete discussion & schedule can be found in
- http://lists.openstack.org/pipermail/openstack-discuss/2019-October/010142.html
- https://etherpad.openstack.org/p/drop-python2-support

Ussuri Communtiy-wide goal:
https://governance.openstack.org/tc/goals/selected/ussuri/drop-py27.html

Change-Id: Ib769d9cbb7ba9f191014c5445ed7f289e013aef4

.zuul.d/jobs.yaml

@@ -1,7 +1,6 @@
 - project:
     templates:
-      - openstack-python-jobs
-      - openstack-python3-train-jobs
+      - openstack-python3-ussuri-jobs
       - publish-openstack-docs-pti
       - release-notes-jobs-python3
     check:

releasenotes/notes/drop-python2.7-064c5e5bcfb4539c.yaml

@@ -0,0 +1,4 @@
+---
+deprecations:
+  - |
+    bashate is now Python 3 only and no longer supports Python 2.

setup.cfg

@@ -6,6 +6,7 @@ description-file =
 author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 home-page = http://docs.openstack.org/developer/bashate/
+python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -13,8 +14,6 @@ classifier =
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     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

test-requirements.txt

@@ -9,8 +9,7 @@ coverage>=3.6
 discover
 fixtures>=1.3.1
 python-subunit>=0.0.18
-sphinx!=1.6.6,!=1.6.7,<2.0.0;python_version=='2.7'  # BSD
-sphinx!=1.6.6,!=1.6.7,!=2.1.0;python_version>='3.4'  # BSD
+sphinx!=1.6.6,!=1.6.7,!=2.1.0  # BSD
 openstackdocstheme>=1.11.0 # Apache-2.0
 testtools>=2.2.0
 stestr>=1.0.0 # Apache-2.0

tox.ini

@@ -1,9 +1,11 @@
 [tox]
-minversion = 2.0
-envlist = py27,py36,py37,pep8
+minversion = 3.1.1
+envlist = py36,py37,pep8
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install -U {opts} {packages}
 setenv =
@@ -15,15 +17,12 @@ commands =
    stestr run --slowest {posargs}
 
 [testenv:pep8]
-basepython = python3
 commands = flake8
 
 [testenv:docs]
-basepython = python3
 commands = python setup.py build_sphinx
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:cover]
@@ -39,7 +38,6 @@ commands =
   coverage report
 
 [testenv:releasenotes]
-basepython = python3
 commands = sphinx-build -a -W -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [flake8]
@@ -53,7 +51,6 @@ exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build
 # This environment can be used to quickly validate that all needed system
 # packages required to successfully execute test targets are installed
 [testenv:bindep]
-basepython = python3
 # Do not install any requirements. We want this to be fast and work even if
 # system dependencies are missing, since it's used to tell you what system
 # dependencies are missing! This also means that bindep must be installed