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

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

masakari-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

Change-Id: I9d3f6dc7490a8cca70ddb2ebd42b94cb86d6304b

.zuul.yaml

@@ -2,6 +2,5 @@
     templates:
       - check-requirements
       - horizon-non-primary-django-jobs
-      - openstack-python-jobs
-      - openstack-python3-train-jobs
+      - openstack-python3-ussuri-jobs
       - release-notes-jobs-python3

releasenotes/notes/drop-py-2-7-a5322c1cb7c74c61.yaml

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

setup.cfg

@@ -13,8 +13,6 @@ 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

tox.ini

@@ -1,9 +1,11 @@
 [tox]
 envlist = pep8,py27,py36,py37,py3-{dj111,dj22}
-minversion = 2.0
+minversion = 3.1.1
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 setenv = VIRTUAL_ENV={envdir}
          BRANCH_NAME=master
@@ -23,15 +25,12 @@ commands =
    python manage.py test {posargs} --settings=masakaridashboard.test.settings --verbosity 2
 
 [testenv:pep8]
-basepython = python3
 commands = flake8 {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:cover]
-basepython = python3
 commands =
   coverage erase
   coverage run {toxinidir}/manage.py test masakaridashboard --settings=masakaridashboard.test.settings {posargs}
@@ -39,7 +38,6 @@ commands =
   coverage html --omit '.tox/cover/*' -d 'cover/htmlcov'
 
 [testenv:eslint]
-basepython = python3
 whitelist_externals = npm
 commands =
   npm install
@@ -47,7 +45,6 @@ commands =
   npm run lint
 
 [testenv:karma]
-basepython = python3
 # NOTE(shu-mutou): Until PhantomJS setup get reliable, we use
 # Chromium for JS test. And npm can't launch Chromium via tox.
 #whitelist_externals = npm
@@ -61,7 +58,6 @@ commands =
   echo "nexecute `npm run test`"
 
 [testenv:docs]
-basepython = python3
 # We need to install horizon dependencies to build module references
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
@@ -71,7 +67,6 @@ commands =
   sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:releasenotes]
-basepython = python3
 # There is no need to install horizon.
 usedevelop = False
 deps =