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: I368d1fe36117bd39b89c14a758bd0cf4fc567031
Story: #2005924
Task: #34225

setup.cfg

@@ -16,7 +16,8 @@ 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

@@ -1,6 +1,6 @@
 [tox]
 minversion = 2.0
-envlist = py35,py27,pep8
+envlist = py27,py37,pep8
 skipsdist = True
 
 [testenv]

zuul.d/project.yaml

@@ -3,8 +3,7 @@
       - openstack-lower-constraints-jobs-neutron
       - openstack-python-jobs-neutron
       - publish-openstack-docs-pti
-      - openstack-python35-jobs-neutron
-      - openstack-python36-jobs-neutron
+      - openstack-python3-train-jobs-neutron
       - release-notes-jobs-python3
     check:
       jobs:
@@ -17,10 +16,10 @@
         - openstack-tox-py27:
             required-projects:
               - openstack/neutron-lib
-        - openstack-tox-py35:
+        - openstack-tox-py36:
             required-projects:
               - openstack/neutron-lib
-        - openstack-tox-py36:
+        - openstack-tox-py37:
             required-projects:
               - openstack/neutron-lib
     gate:
@@ -34,9 +33,9 @@
         - openstack-tox-py27:
             required-projects:
               - openstack/neutron-lib
-        - openstack-tox-py35:
-            required-projects:
-              - openstack/neutron-lib
         - openstack-tox-py36:
             required-projects:
-              - openstack/neutron-lib
+              - openstack/neutron-lib
+        - openstack-tox-py37:
+            required-projects:
+              - openstack/neutron-lib