Stop testing with py2 and switch to ussuri jobs

Remove py2 from tox.ini, setup.cfg, and zuul.

Switch from train to ussuri zuul job template.

Change-Id: I70eeabe2237c3f13b7e7a27fb32c9d2cd1609333

.zuul.yaml

@@ -1,7 +1,6 @@
 - project:
     templates:
-      - openstack-python-jobs
       - publish-openstack-docs-pti
       - check-requirements
-      - openstack-python3-train-jobs
+      - openstack-python3-ussuri-jobs
       - release-notes-jobs-python3

doc/source/user/index.rst

@@ -6,12 +6,12 @@ Usage
 by simply importing the ``os_traits`` module and referencing one of the
 module's traits constants::
 
-    $ python
-    Python 2.7.11+ (default, Apr 17 2016, 14:00:29)
-    [GCC 5.3.1 20160413] on linux2
+    $ python3
+    Python 3.6.8 (default, Oct  7 2019, 12:59:55)
+    [GCC 8.3.0] on linux
     Type "help", "copyright", "credits" or "license" for more information.
     >>> import os_traits as ot
-    >>> print ot.HW_CPU_X86_SSE42
+    >>> print(ot.HW_CPU_X86_SSE42)
     HW_CPU_X86_SSE42
 
 You can get a list of the ``os_traits`` symbols by simply doing a

releasenotes/notes/drop-python2-support-d11499973c50713b.yaml

@@ -0,0 +1,4 @@
+---
+upgrade:
+  - |
+    Python 2 is no longer supported. Python 3 is required.

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

@@ -1,8 +1,9 @@
 [tox]
 minversion = 2.0
-envlist = py27,py37,pep8
+envlist = py37,pep8
 
 [testenv]
+basepython = python3
 install_command = pip install {opts} {packages}
 whitelist_externals =
   rm
@@ -12,15 +13,12 @@ deps =
 commands = stestr run --slowest {posargs}
 
 [testenv:pep8]
-basepython = python3
 commands = flake8 {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:docs]
-basepython = python3
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
   -r{toxinidir}/doc/requirements.txt
@@ -29,7 +27,6 @@ commands =
   sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:pdf-docs]
-basepython = python3
 deps = {[testenv:docs]deps}
 whitelist_externals =
   make
@@ -38,7 +35,6 @@ commands =
   make -C doc/build/pdf
 
 [testenv:releasenotes]
-basepython = python3
 deps =
   {[testenv:docs]deps}
 commands =
@@ -46,7 +42,6 @@ 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]