Update tox.ini for wallaby supported pythons

The wallaby PTI specifies python 3.6 and 3.8 as the supported
wallaby versions.

Change-Id: I51b7a7a36c1478d261eb0eba948803f3f614b4f0

.zuul.yaml

@@ -52,10 +52,10 @@
       tox_envlist: functional-py36
 
 - job:
-    name: brick-cinderclient-dsvm-functional-py37
+    name: brick-cinderclient-dsvm-functional-py38
     parent: brick-cinderclient-dsvm-functional-base
     vars:
-      tox_envlist: functional-py37
+      tox_envlist: functional-py38
 
 - project:
     templates:
@@ -67,8 +67,8 @@
     check:
       jobs:
         - brick-cinderclient-dsvm-functional-py36
-        - brick-cinderclient-dsvm-functional-py37
+        - brick-cinderclient-dsvm-functional-py38
     gate:
       jobs:
         - brick-cinderclient-dsvm-functional-py36
-        - brick-cinderclient-dsvm-functional-py37
+        - brick-cinderclient-dsvm-functional-py38

tox.ini

@@ -2,7 +2,7 @@
 minversion = 3.1.0
 skipsdist = True
 skip_missing_interpreters = true
-# python runtimes: https://governance.openstack.org/tc/reference/runtimes/ussuri.html
+# python runtimes: https://governance.openstack.org/tc/reference/project-testing-interface.html#tested-runtimes
 envlist = py38,py36,pep8
 # this allows tox to infer the base python from the environment name
 # and override any basepython configured in this file
@@ -48,7 +48,7 @@ passenv = OS_*
 setenv =
   {[testenv:functional]setenv}
 
-[testenv:functional-py37]
+[testenv:functional-py38]
 setenv =
   {[testenv:functional]setenv}