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

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

mistral-dashboard 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

Depends-On: https://review.opendev.org/#/c/693631/
Change-Id: Ib39cbe4f526d5ace03f959e21eb4907c97ac7b65

.zuul.yaml

@@ -1,6 +1,5 @@
 - project:
     templates:
       - horizon-non-primary-django-jobs
-      - openstack-python-jobs
       - check-requirements
       - openstack-python3-ussuri-jobs

doc/requirements.txt

@@ -1,4 +1,3 @@
-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,!=2.1.0,>=1.6.2;python_version>='3.4' # BSD
 oslosphinx>=4.7.0 # Apache-2.0
 reno>=2.5.0 # Apache-2.0

releasenotes/notes/drop-py-2-7-022d0dd59feb8b07.yaml

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

setup.cfg

@@ -5,8 +5,6 @@ description-file = README.rst
 license = Apache License, Version 2.0
 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 +1,10 @@
 [tox]
 minversion = 2.0
-envlist = pep8,py27,py37,py3-{dj111,dj22}
+envlist = pep8,py37,py3-{dj111,dj22}
 skipsdist = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
 setenv =
@@ -18,20 +19,14 @@ commands =
     /bin/bash run_tests.sh -N --no-pep8 {posargs}
 whitelist_externals = find
 
-[testenv:py27]
-setenv = DJANGO_SETTINGS_MODULE=mistraldashboard.test.settings
-
 [testenv:pep8]
-basepython = python3
 commands =
     flake8
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:cover]
-basepython = python3
 setenv =
     PYTHON=coverage run --source mistraldashboard --parallel-mode
 commands =
@@ -41,7 +36,6 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:docs]
-basepython = python3
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/requirements.txt
@@ -50,7 +44,6 @@ commands =
   sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:debug]
-basepython = python3
 whitelist_externals = oslo_debug_helper
 commands = oslo_debug_helper -t mistraldashboard/test {posargs}
 
@@ -59,7 +52,6 @@ show-source = True
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build,.ropeproject,tools,horizon
 
 [testenv:releasenotes]
-basepython = python3
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/requirements.txt