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

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

python-monascaclient 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: If739012908f458acccba1e40fe6bb8dbd231fca7

.zuul.yaml

@@ -2,7 +2,6 @@
     templates:
       - openstack-cover-jobs
       - openstack-lower-constraints-jobs
-      - openstack-python-jobs
       - openstack-python3-ussuri-jobs
       - publish-openstack-docs-pti
       - check-requirements

releasenotes/notes/drop-py-2-7-1c41855c5edc5ba3.yaml

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

test-requirements.txt

@@ -13,7 +13,6 @@ testtools>=2.2.0 # MIT
 
 # documentation
 doc8>=0.6.0 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,>=1.6.5,<2.0.0;python_version=='2.7' # BSD
 sphinx!=1.6.6,!=1.6.7,!=2.1.0,>=1.6.5;python_version>='3.4' # BSD
 reno>=2.5.0 # Apache-2.0
 openstackdocstheme>=1.18.1 # Apache-2.0

tox.ini

@@ -1,9 +1,11 @@
 [tox]
-envlist = py27,py37,pypy,cover,pep8
-minversion = 2.5
+envlist = py37,pypy,cover,pep8
+minversion = 3.1.1
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 setenv =
     VIRTUAL_ENV={envdir}
     OS_TEST_PATH=monascaclient/tests
@@ -24,7 +26,6 @@ commands =
   stestr run {posargs}
 
 [testenv:cover]
-basepython = python3
 setenv =
     PYTHON=coverage run --source monascaclient --parallel-mode
 commands =
@@ -36,11 +37,9 @@ commands =
     coverage report
 
 [testenv:debug]
-basepython = python3
 commands = oslo_debug_helper -t {env:OS_TEST_PATH} {posargs}
 
 [testenv:pep8]
-basepython = python3
 skip_install = True
 usedevelop = False
 commands =
@@ -49,48 +48,41 @@ commands =
   {[testenv:checkniceness]commands}
 
 [testenv:flake8]
-basepython = python3
 skip_install = True
 usedevelop = False
 commands = flake8 monascaclient
 
 [testenv:bandit]
-basepython = python3
 skip_install = True
 usedevelop = False
 commands = bandit -r monascaclient -n5 -x {env:OS_TEST_PATH}
 
 [testenv:docs]
-basepython = python3
 description = Builds full monascaclient documentation
 commands =
   {[testenv:devdocs]commands}
   {[testenv:releasenotes]commands}
 
 [testenv:devdocs]
-basepython = python3
 description = Builds developer documentation
 commands =
   rm -rf {toxinidir}/doc/build {toxinidir}/doc/source/contributor/api
   python setup.py build_sphinx
 
 [testenv:releasenotes]
-basepython = python3
 description = Called from CI script to test and publish the Release Notes
 commands =
   rm -rf releasenotes/build
   sphinx-build -a -E -d {toxinidir}/releasenotes/build/doctrees -b html \
     {toxinidir}/releasenotes/source {toxinidir}/releasenotes/build/html
 
 [testenv:checkniceness]
-basepython = python3
 description = Validates (pep-like) documenation
 commands =
   doc8 --file-encoding utf-8 {toxinidir}/doc
   doc8 --file-encoding utf-8 {toxinidir}/releasenotes
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [hacking]
@@ -104,7 +96,6 @@ builtins = _
 exclude=.venv,.git,.tox,dist,client_api_example.py,*lib/python*,*egg,build
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt