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: I13689a385bf237681bc96f3cc62fc17864f12659

.zuul.yaml

@@ -14,9 +14,8 @@
     templates:
       - openstack-cover-jobs
       - openstack-python-jobs
-      - openstack-python35-jobs
       - docs-on-readthedocs
-      - openstack-python36-jobs
+      - openstack-python3-train-jobs
     vars:
       rtd_webhook_id: '38572'
       rtd_project_name: 'airship-deckhand'

setup.cfg

@@ -15,8 +15,8 @@ classifier =
     Programming Language :: Python :: 2
     Programming Language :: Python :: 2.7
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
 
 [files]
 packages =

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 minversion = 2.3.1
 skipsdist = True
-envlist = py{36,35,27},py{36,35,27}-{postgresql},functional,cover,pep8,bandit,docs
+envlist = py{37,36,27},py{37,36,27}-{postgresql},functional,cover,pep8,bandit,docs
 
 [testenv]
 usedevelop = True