remove py27 in tox.ini from paunch

Remove python 2 from envlist parameter. Check the link:

https://etherpad.openstack.org/p/drop-python2-support
https://governance.openstack.org/tc/goals/selected/ussuri/drop-py27.html

The plan is drop the python 2 support from OpenStack in Ussuri release.
Move the basepython parameter.

Change-Id: I78a9fa945fb8f680a62f68e4b10833e0be233ee6

tox.ini

@@ -1,9 +1,10 @@
 [tox]
 minversion = 2.0
-envlist = pep8,py27,py37
+envlist = pep8,py37
 skipsdist = False
 
 [testenv]
+basepython = python3
 setenv = VIRTUAL_ENV={envdir}
 deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/requirements.txt
@@ -17,15 +18,12 @@ commands =
     stestr run {posargs}
 
 [testenv:pep8]
-basepython = python3
 commands = flake8 {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:cover]
-basepython = python3
 setenv =
   PYTHON=coverage run --source paunch --parallel-mode
   HOME={envdir}
@@ -38,19 +36,16 @@ commands =
   coverage report
 
 [testenv:docs]
-basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands = python setup.py build_sphinx
 
 [testenv:releasenotes]
-basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:debug]
-basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [flake8]

zuul.d/layout.yaml

@@ -8,13 +8,11 @@
     check:
       jobs:
         - openstack-tox-pep8
-        - openstack-tox-py27
         - openstack-tox-py36
         - openstack-tox-py37
         - tripleo-ci-centos-8-scenario004-standalone:
             dependencies:
               - openstack-tox-pep8
-              - openstack-tox-py27
               - openstack-tox-py36
               - openstack-tox-py37
             irrelevant-files: &standalone_ignored