Updated Zuul and tox configuration.

Change-Id: I003a5163a38bee1196626ffb69d5f5b23782dcfc

setup.cfg

@@ -14,8 +14,9 @@ classifier =
     Operating System :: POSIX :: Linux
     Programming Language :: Python
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
 
 [files]
 packages =

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 2.3.1
-envlist = py38,pep8
+envlist = py36,py37,py38,pep8
 skipsdist = True
 
 [testenv]
@@ -38,6 +38,12 @@ commands =
 commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
+[testenv:py36]
+basepython = python3.6
+
+[testenv:py37]
+basepython = python3.7
+
 [testenv:py38]
 basepython = python3.8
 

zuul.d/projects.yaml

@@ -1,5 +1,7 @@
 - project:
     templates:
+      - openstack-python36-jobs-no-constraints
+      - openstack-python37-jobs-no-constraints
       - openstack-python38-jobs-no-constraints
       - check-requirements
       - publish-to-pypi