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: I10050c3ff90a0b7a9a905958194c06cc8db7473a
Story: #2005924
Task: #34223

.zuul.yaml

@@ -4,8 +4,7 @@
       - openstack-cover-jobs
       - openstack-lower-constraints-jobs
       - openstack-python-jobs
-      - openstack-python36-jobs
-      - openstack-python37-jobs
+      - openstack-python3-train-jobs
       - release-notes-jobs-python3
     check:
       jobs:

setup.cfg

@@ -7,6 +7,13 @@ classifier=
   Development Status :: 5 - Production/Stable
   License :: OSI Approved :: Apache Software License
   Topic :: System :: Monitoring
+  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
+
 keywords = openstack monitoring storage
 description-file = README.rst
 home-page = https://github.com/openstack/monasca-persister

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27,py36,pep8
+envlist = py27,py37,pep8
 minversion = 2.1
 skipsdist = True