Add Python 3 Train unit tests

This is a mechanically generated patch to ensure unit testing is in place
for all of the Tested Runtimes for Train.

See the Train python3-updates goal document for details:
https://governance.openstack.org/tc/goals/train/python3-updates.html

Change-Id: Iee35ef61a46fd6a318f9b0b1d4e6436d5fd3c008
Story: #2005924
Task: #34234

.zuul.yaml

@@ -6,8 +6,7 @@
       - openstack-lower-constraints-jobs
       - openstack-cover-jobs
       - openstack-python-jobs
-      - openstack-python36-jobs
-      - openstack-python37-jobs
+      - openstack-python3-train-jobs
       - periodic-stable-jobs
       - publish-openstack-docs-pti
       - release-notes-jobs-python3

setup.cfg

@@ -19,6 +19,7 @@ classifier =
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
     Topic :: Software Development :: Libraries
     Topic :: System :: Distributed Computing
 

tox.ini

@@ -1,14 +1,6 @@
 [tox]
 minversion = 2.0
-envlist =
-  cover,
-  docs,
-  pep8,
-  py27,
-  py36,
-  py37,
-  pylint,
-  update-states
+envlist = cover,docs,pep8,py27,py37,pylint,update-states
 
 [testenv]
 setenv =