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

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

mistral-extra 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

Depends-On: https://review.opendev.org/#/c/693631/
Change-Id: I32edd618a65f5ef65be1c7894dd4f52c97f733c3

.zuul.yaml

@@ -1,5 +1,4 @@
 - project:
     templates:
-      - openstack-python-jobs
       - openstack-python3-ussuri-jobs
       - check-requirements

releasenotes/notes/drop-py-2-7-0d2aa8bcea5ff645.yaml

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

setup.cfg

@@ -14,8 +14,6 @@ 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

test-requirements.txt

@@ -5,7 +5,6 @@
 hacking>=1.1.0,<1.2.0 # Apache-2.0
 coverage>=4.0 # Apache-2.0
 python-subunit>=0.0.18 # Apache-2.0/BSD
-sphinx>=1.8.0,<2.0.0;python_version=='2.7' # BSD
 sphinx>=1.8.0,!=2.1.0;python_version>='3.4' # BSD
 oslosphinx>=4.7.0 # Apache-2.0
 oslotest>=1.10.0 # Apache-2.0

tox.ini

@@ -1,9 +1,10 @@
 [tox]
 minversion = 2.0
-envlist = py27,py37,pep8
+envlist = py37,pep8
 skipsdist = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install {opts} {packages}
 deps =
@@ -13,16 +14,13 @@ deps =
 commands = stestr run --slowest {posargs}
 
 [testenv:pep8]
-basepython = python3
 commands =
     flake8 {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:cover]
-basepython = python3
 setenv =
     PYTHON=coverage run --source $project --parallel-mode
 commands =
@@ -32,11 +30,9 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:docs]
-basepython = python3
 commands = python setup.py build_sphinx
 
 [testenv:releasenotes]
-basepython = python3
 whitelist_externals =
   rm
 commands =
@@ -44,7 +40,6 @@ commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
 
 [testenv:debug]
-basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [flake8]