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

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

python-karborclient 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: I777e4ecb3dbb1bea98a9a8c2e5bde1ee4129cc0f

.zuul.yaml

@@ -3,7 +3,6 @@
       - check-requirements
       - openstack-cover-jobs
       - openstack-lower-constraints-jobs
-      - openstack-python-jobs
-      - openstack-python3-train-jobs
+      - openstack-python3-ussuri-jobs
       - openstackclient-plugin-jobs
       - publish-openstack-docs-pti

releasenotes/notes/drop-py-2-7-7a92a5906980666b.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    Python 2.7 support has been dropped. Last release of python-karborclient
+    to support python 2.7 is OpenStack Train. The minimum version of Python now
+    supported 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]
-minversion = 2.0
-envlist = py27,py37,pypy,pep8
+minversion = 3.1.1
+envlist = py37,pypy,pep8
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install {opts} {packages}
 setenv =
@@ -19,28 +21,23 @@ commands =
   python setup.py test --slowest --testr-args='{posargs}'
 
 [testenv:pep8]
-basepython = python3
 commands = flake8
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:cover]
-basepython = python3
 commands =
   python setup.py test --coverage --testr-args='{posargs}'
   coverage report
 
 [testenv:docs]
-basepython = python3
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:debug]
-basepython = python3
 commands = oslo_debug_helper -t karborclient/tests {posargs}
 
 [flake8]
@@ -51,7 +48,6 @@ builtins = _
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,tools
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt