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

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

Mistral 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: Ica51b3b36f3784b4b04731406b6bf8320d5de4b8

.zuul.yaml

@@ -3,6 +3,8 @@
     parent: devstack
     timeout: 7800
     vars:
+      devstack_localrc:
+        USE_PYTHON3: true
       devstack_plugins:
         mistral: https://opendev.org/openstack/mistral
         heat: https://opendev.org/openstack/heat
@@ -34,6 +36,8 @@
       devstack_plugins:
         rally-openstack: https://opendev.org/openstack/rally-openstack
       rally_task: rally-jobs/task-mistral.yaml
+      devstack_localrc:
+        USE_PYTHON3: true
     required-projects:
       - openstack/rally-openstack
 
@@ -90,7 +94,6 @@
 
 - project:
     templates:
-      - openstack-python-jobs
       - openstack-python3-ussuri-jobs
       - publish-openstack-docs-pti
       - check-requirements
@@ -112,9 +115,6 @@
         - openstack-tox-py37:
             required-projects:
               - openstack/mistral-lib
-        - openstack-tox-py27:
-            required-projects:
-              - openstack/mistral-lib
         - mistral-devstack
         - mistral-devstack-non-apache
         - mistral-devstack-kombu

playbooks/legacy/mistral-ha/run.yaml

@@ -48,6 +48,7 @@
           # mistral with "check experimental" and trigger the gate). After
           # it's ready it'll be better to create a special builder in this
           # file.
+          export DEVSTACK_GATE_USE_PYTHON3=True
           ha_gate/install.sh
           ha_gate/run_tests.sh
         chdir: '{{ ansible_user_dir }}/workspace'

releasenotes/notes/drop-py-2-7-d6ce46d3dc571c01.yaml

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

setup.cfg

@@ -7,8 +7,6 @@ license = Apache License, Version 2.0
 home-page = https://docs.openstack.org/mistral/latest/
 classifiers =
     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 +1,10 @@
 [tox]
-envlist = py27,py37,pep8
+envlist = py37,pep8
 minversion = 2.0
 skipsdist = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
@@ -25,25 +26,21 @@ whitelist_externals =
   find
 
 [testenv:unit-postgresql]
-basepython = python3
 setenv = VIRTUAL_ENV={envdir}
 passenv = ZUUL_PROJECT
 commands = ./run_tests.sh -N --db-type postgresql
 
 [testenv:unit-mysql]
-basepython = python3
 setenv = VIRTUAL_ENV={envdir}
 passenv = ZUUL_PROJECT
 commands = ./run_tests.sh -N --db-type mysql
 
 [testenv:pep8]
-basepython = python3
 commands =
   doc8 doc/source
   flake8 {posargs} . {toxinidir}/tools/get_action_list.py {toxinidir}/tools/sync_db.py
 
 [testenv:cover]
-basepython = python3
 setenv =
     {[testenv]setenv}
     PYTHON=coverage run --source mistral --parallel-mode
@@ -54,26 +51,22 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:genconfig]
-basepython = python3
 commands =
     oslo-config-generator --config-file tools/config/config-generator.mistral.conf \
     --output-file etc/mistral.conf.sample
 
 [testenv:genpolicy]
-basepython = python3
 commands =
     oslopolicy-sample-generator --config-file tools/config/policy-generator.mistral.conf \
     --output-file etc/policy.yaml.sample
 
 #set PYTHONHASHSEED=0 to prevent wsmeext.sphinxext from randomly failing.
 [testenv:venv]
-basepython = python3
 setenv = PYTHONHASHSEED=0
 commands = {posargs}
 
 #set PYTHONHASHSEED=0 to prevent wsmeext.sphinxext from randomly failing.
 [testenv:docs]
-basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 setenv = PYTHONHASHSEED=0
 commands =
@@ -81,7 +74,6 @@ commands =
   sphinx-build -E -W --keep-going -b html doc/source doc/build/html
 
 [testenv:pdf-docs]
-basepython = python3
 deps = -r{toxinidir}/doc/requirements.txt
 whitelist_externals =
   make
@@ -90,13 +82,11 @@ commands =
   make -C doc/build/pdf
 
 [testenv:releasenotes]
-basepython = python3
 commands =
   rm -rf releasenotes/build
   sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
 
 [testenv:api-ref]
-basepython = python3
 # This environment is called from CI scripts to test and publish
 # the API Ref to docs.openstack.org.
 commands =
@@ -125,7 +115,6 @@ local-check-factory = mistral.hacking.checks.factory
 import_exceptions = mistral._i18n
 
 [testenv:lower-constraints]
-basepython = python3
 deps =
   -c{toxinidir}/lower-constraints.txt
   -r{toxinidir}/test-requirements.txt