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

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

heat-dashboard is ready with python 3 and ok to drop the
python 2.7 support.

Also this patch update minimum tox version in tox.ini file.
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: I63d6c5dfb2bb312c413b9350fa7c9a01eae6cd0b

.zuul.yaml

@@ -27,7 +27,6 @@
       - horizon-non-primary-django-jobs
       - horizon-nodejs10-jobs
       - openstack-lower-constraints-jobs
-      - openstack-python-jobs-horizon
       - openstack-python3-ussuri-jobs-horizon
       - publish-openstack-docs-pti
       - release-notes-jobs-python3

doc/requirements.txt

@@ -3,7 +3,6 @@
 # process, which may cause wedges in the gate later.
 
 openstackdocstheme>=1.18.1 # 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
 reno>=2.5.0 # Apache-2.0
 sphinxcontrib-httpdomain>=1.3.0 # BSD

releasenotes/notes/drop-py-2-7-3dafc6e9e6f29bda.yaml

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

setup.cfg

@@ -6,6 +6,7 @@ description-file =
 author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 home-page = https://docs.openstack.org/heat-dashboard/latest/
+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

tox.ini

@@ -1,10 +1,12 @@
 [tox]
-envlist = py27,py36,py37,py3-{dj111,dj22},pep8,releasenotes
+envlist = py36,py37,py3-{dj111,dj22},pep8,releasenotes
-minversion = 2.5.0
+minversion = 3.1.1
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
 usedevelop = True
+basepython = python3
 setenv =
   VIRTUAL_ENV={envdir}
   INTEGRATION_TESTS=0
@@ -29,19 +31,15 @@ setenv =
   INTEGRATION_TESTS=1
   SELENIUM_HEADLESS=1
   HORIZON_INTEGRATION_TESTS_CONFIG_FILE=heat_dashboard/test/integration/horizon.conf
-basepython = python2.7
 commands = python manage.py test heat_dashboard.test.integration --settings=heat_dashboard.test.settings --tag integration
 
 [testenv:pep8]
-basepython = python3
 commands = flake8 {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:cover]
-basepython = python3
 commands =
   coverage erase
   coverage run --source=heat_dashboard {toxinidir}/manage.py test heat_dashboard.test.tests --settings=heat_dashboard.test.settings {posargs}
@@ -49,13 +47,11 @@ commands =
   coverage html
 
 [testenv:docs]
-basepython = python3
 deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/doc/requirements.txt
 commands = python setup.py build_sphinx
 
 [testenv:releasenotes]
-basepython = python3
 deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
@@ -75,7 +71,6 @@ max-complexity = 20
 import-order-style = pep8
 
 [testenv:npm]
-basepython = python3
 passenv =
   HOME
   DISPLAY
@@ -97,7 +92,6 @@ max-line-length = 80
 ignore = D000
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt