[ussuri][goal] Drop python 2.7

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

openstack ansible also drops python 2.7 support
and cleanup tox and requirements for python2.

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: I909ef41d8a8d857c56ed93a142d2ff951a9bf1ba

doc/requirements.txt

@@ -3,8 +3,7 @@
 # process, which may cause wedges in the gate later.
 
 # this is required for the docs build jobs
-sphinx>=1.8.0,<2.0.0;python_version=='2.7' # BSD
-sphinx>=1.8.0,!=2.1.0;python_version>='3.4'  # BSD
+sphinx>=1.8.0,!=2.1.0 # BSD
 sphinxcontrib-svg2pdfconverter>=0.1.0 # BSD
 openstackdocstheme>=1.29.2 # Apache-2.0
 reno>=2.11.3 # Apache-2.0

releasenotes/notes/drop-py-2-7-ff5e69d0456fbf4c.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    Python 2.7 support has been dropped. Last release of openstack ansible
+    to support python 2.7 is OpenStack Train.

requirements.txt

@@ -3,7 +3,6 @@
 # process, which may cause wedges in the gate later.
 pyasn1!=0.2.3,>=0.1.8 # BSD
 pyOpenSSL>=17.1.0 # Apache-2.0
-ndg-httpsclient>=0.4.2;python_version<'3.0' # BSD
 netaddr>=0.7.18 # BSD
 PrettyTable<0.8,>=0.7.1 # BSD
 python-memcached>=1.56 # PSF

tox.ini

@@ -1,11 +1,12 @@
 [tox]
-minversion = 2.0
+minversion = 3.1
 skipsdist = True
 envlist = linters,docs,releasenotes,inventory,py3-inventory
+ignore_basepython_conflict = True
 
 [testenv]
 usedevelop = True
-basepython = python2.7
+basepython = python3
 install_command =
     pip install -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/upper-constraints.txt} {opts} {packages}
 deps =
@@ -36,19 +37,16 @@ setenv =
     ANSIBLE_LINT_PARAMS=--exclude={homedir}/.ansible/roles
 
 [testenv:docs]
-basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
     doc8 doc
     docstheme-build-translated.sh
 
 [testenv:deploy-guide]
-basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -a -E -W -d deploy-guide/build/doctrees --keep-going -b html deploy-guide/source deploy-guide/build/html
 
 [testenv:pdf-docs]
-basepython = python3
 deps = {[testenv:docs]deps}
 whitelist_externals =
   make
@@ -62,19 +60,16 @@ extensions = .rst
 ignore = D001
 
 [testenv:releasenotes]
-basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 commands =
     sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
 
 # environment used by the -infra templated docs job
 [testenv:venv]
-basepython = python3
 commands =
     {posargs}
 
 [testenv:pep8]
-basepython = python3
 commands =
     bash -c "{toxinidir}/tests/common/test-pep8.sh"
 
@@ -85,7 +80,6 @@ commands =
 ignore=F403
 
 [testenv:bashate]
-basepython = python3
 commands =
     bash -c "{toxinidir}/tests/common/test-bashate.sh"
 
@@ -99,28 +93,24 @@ commands =
 # or for a stable branch:
 # https://opendev.org/openstack/openstack-ansible-tests/raw/stable/stein/test-ansible-deps.txt
 [testenv:ansible]
-basepython = python3
 deps =
     {[testenv]deps}
     -r{toxinidir}/global-requirement-pins.txt
     -rhttps://opendev.org/openstack/openstack-ansible-tests/raw/test-ansible-deps.txt
 
 [testenv:ansible-syntax]
-basepython = python3
 deps =
     {[testenv:ansible]deps}
 commands =
     bash -c "{toxinidir}/tests/common/test-ansible-syntax.sh"
 
 [testenv:ansible-lint]
-basepython = python3
 deps =
     {[testenv:ansible]deps}
 commands =
     bash -c "{toxinidir}/tests/common/test-ansible-lint.sh"
 
 [testenv:inventory]
-basepython = python3
 # Use a fixed seed since some inventory tests rely on specific ordering
 setenv =
     {[testenv]setenv}
@@ -135,14 +125,12 @@ commands =
     coverage report --show-missing --include={toxinidir}/inventory/*,{toxinidir}/osa_toolkit/*
 
 [testenv:py3-inventory]
-basepython = python3.5
 setenv =
     {[testenv:inventory]setenv}
 commands =
     {[testenv:inventory]commands}
 
 [testenv:linters]
-basepython = python3
 deps =
     {[testenv:ansible]deps}
 commands =