Drop python2 and 3.5, update jobs to python3

OpenStack has dropped the py2.7 and py3.5 support in ussuri cycle.

From now on, refstack will test all stable branches with py3 jobs.
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

Story: 2003257
Task: 24062
Change-Id: I90ab2eca6366f0b6256f097712efac2ffe08b2c0

.zuul.yaml

@@ -6,31 +6,14 @@
       # Disable since it fails
       # - openstack-python-jobs
       # - openstack-python35-jobs
-      - openstack-python36-jobs
+      - openstack-python3-wallaby-jobs
     check:
       jobs:
-        - refstack-tox-py27-func-mysql:
-            voting: false
         - refstack-tox-py36-func-mysql
     gate:
       jobs:
-        # - refstack-tox-py27-func-mysql
         - refstack-tox-py36-func-mysql
 
-- job:
-    name: refstack-tox-py27-func-mysql
-    parent: openstack-tox
-    description: |
-      Run unit tests for an OpenStack Python project under cPython version 2.7.
-
-      Uses tox with the ``py27-func-mysql`` environment.
-    irrelevant-files:
-      - ^.*\.rst$
-      - ^doc/.*$
-      - ^releasenotes/.*$
-    vars:
-      tox_envlist: py27-func-mysql
-
 - job:
     name: refstack-tox-py36-func-mysql
     parent: openstack-tox

requirements.txt

@@ -12,7 +12,7 @@ six>=1.9.0 # MIT
 pecan>=0.8.2
 requests>=2.2.0,!=2.4.0
 requests-cache>=0.4.9
-jsonschema>=2.0.0,<3.0.0
+jsonschema>=3.2.0
 PyJWT>=1.0.1  # MIT
 WebOb>=1.7.1  # MIT
 PyMySQL>=0.6.2,!=0.6.4

setup.cfg

@@ -13,10 +13,8 @@ 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 :: 3.5
+    Programming Language :: Python :: 3.6
 
 [files]
 packages =

tox.ini

@@ -1,12 +1,10 @@
 [tox]
-# py3* tests should be run before py27
-# it is a workaround for testr bug
-# https://bugs.launchpad.net/testrepository/+bug/1229445
-envlist = py35,py36,py27,pep8,pip-check-reqs
-minversion = 1.6
+envlist = py36,pep8,pip-check-reqs
+minversion = 2.0
 skipsdist = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} -U {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
@@ -19,15 +17,6 @@ commands = /bin/rm -f .testrepository/times.dbm
            python setup.py testr --slowest --testr-args='{posargs}'
 distribute = false
 
-[testenv:py27-func-mysql]
-basepython = python2.7
-setenv = SUBUNIT_TEST_PATH=./refstack/tests/api
-# Integration/functional tests
-# must not be run in parallel (--concurrency=1),
-# because each of these tests
-# require cleanup of database
-commands = {toxinidir}/setup-mysql-tests.sh python setup.py testr --slowest --testr-args='{posargs:--concurrency=1}'
-
 [testenv:py36-func-mysql]
 basepython = python3.6
 setenv = SUBUNIT_TEST_PATH=./refstack/tests/api
@@ -37,7 +26,6 @@ setenv = SUBUNIT_TEST_PATH=./refstack/tests/api
 # require cleanup of database
 commands = {toxinidir}/setup-mysql-tests.sh python setup.py testr --slowest --testr-args='{posargs:--concurrency=1}'
 
-
 [testenv:pep8]
 commands =
   flake8 {posargs}
@@ -90,12 +78,7 @@ commands=
 [testenv:debug]
 commands = oslo_debug_helper -t refstack/tests/unit {posargs}
 
-[testenv:debug35]
-basepython = python3.5
-commands = oslo_debug_helper -t refstack/tests/unit {posargs}
-
 [testenv:bindep]
-basepython = python3
 # Do not install any requirements. We want this to be fast and work even if
 # system dependencies are missing, since it's used to tell you what system
 # dependencies are missing! This also means that bindep must be installed