Drop python 2.7 support and testing

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

trove-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://review.opendev.org/#/c/691178/

Change-Id: I7fcfcb5c32481ad5a5839b98cf35198545d2e6a0

.zuul.yaml

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

releasenotes/notes/drop-py-2-7-ee223d109e3bd38e.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    Python 2.7 support has been dropped. Last release of trove-dashboard
+    to support py2.7 is OpenStack Train. The minimum version of Python now
+    supported by trove-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

@@ -1,10 +1,12 @@
 [tox]
-minversion = 1.6
-envlist = py27,py37,py3-{dj111,dj22},pep8
+minversion = 3.1.1
+envlist = py37,py3-{dj111,dj22},pep8
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
 usedevelop = True
+basepython = python3
 install_command = pip install {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
@@ -16,35 +18,25 @@ commands =
   dj22: pip install django>=2.2,<2.3
   /bin/bash run_tests.sh -N --no-pep8 {posargs}
 
-[testenv:py27]
-setenv = DJANGO_SETTINGS_MODULE=trove_dashboard.test.settings
-
 [testenv:pep8]
-basepython = python3
 commands = flake8
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
-[testenv:py27integration]
-basepython = python2.7
+[testenv:integration]
 commands = /bin/bash run_tests.sh -N --integration --selenium-headless {posargs}
 
 [testenv:cover]
-basepython = python3
 commands = python setup.py testr --coverage --testr-args={posargs}
 
 [testenv:docs]
-basepython = python3
 commands = python setup.py build_sphinx
 
 [testenv:debug]
-basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [testenv:releasenotes]
-basepython = python3
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [flake8]