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: Ic95726f90b549df62d6a3e5312e1fa1dc7e50e48
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
     check:
       jobs:
         - monasca-tempest-python2-influxdb:

setup.cfg

@@ -18,7 +18,9 @@ classifier =
     Topic :: System :: Monitoring
     Programming Language :: Python
     Programming Language :: Python :: 2.7
+    Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
 
 [files]
 packages =

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py{27,36},pep8,cover
+envlist = py27,py37,pep8,cover
 minversion = 2.5
 skipsdist = True