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

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

python-mistralclient 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: Ia2e548105f06dfdd2dbabd425002ea1d4fe57f53

.zuul.yaml

@@ -28,7 +28,6 @@
     templates:
       - check-requirements
       - openstack-lower-constraints-jobs
-      - openstack-python-jobs
       - openstack-python3-ussuri-jobs
       - openstackclient-plugin-jobs
       - publish-openstack-docs-pti

doc/requirements.txt

@@ -1,7 +1,6 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-sphinx>=1.8.0,<2.0.0;python_version=='2.7' # BSD
 sphinx>=1.8.0,!=2.1.0;python_version>='3.4' # BSD
 reno>=2.5.0 # Apache-2.0
 openstackdocstheme>=1.30.0 # Apache-2.0

releasenotes/notes/drop-py-2-7-9c369125c06e32bd.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    Python 2.7 support has been dropped. Last release of python-mistralclient
+    to support python 2.7 is OpenStack Train. The minimum version of Python now
+    supported is Python 3.6.

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

@@ -1,9 +1,11 @@
 [tox]
-envlist = py27,py37,pep8
+envlist = py37,pep8
-minversion = 2.0
+minversion = 3.1.1
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install {opts} {packages}
 setenv =
@@ -29,16 +31,13 @@ commands =
     stestr run --concurrency 1 --slowest {posargs}
 
 [testenv:pep8]
-basepython = python3
 commands =
     flake8 {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:docs]
-basepython = python3
 deps =
     -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
     -r{toxinidir}/requirements.txt
@@ -57,7 +56,6 @@ builtins = _
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,tools
 
 [testenv:releasenotes]
-basepython = python3
 deps =
     -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
     -r{toxinidir}/requirements.txt
@@ -67,7 +65,6 @@ commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt