[goal] Migrate testing to ubuntu focal

If we move horizon jobs to focal then murano-dashboard nodejs jobs
fail. This patch the updates python version to py38 in karma.conf.js
and tools/post_install.sh files as py36 is not avaialbale on focal
which fixes failed nodejs job.

Depends-On: https://review.opendev.org/#/c/744647/

Change-Id: Ic72729514d4759466e8afeac6d03cb1ed7a1765d

karma.conf.js

@@ -21,7 +21,7 @@ var path = require('path');
 
 module.exports = function (config) {
   // This tox venv is setup in the post-install npm step
-  var toxPath = '.tox/py36/lib/python3.6/site-packages/';
+  var toxPath = '.tox/py38/lib/python3.8/site-packages/';
   var xstaticPath = toxPath + 'xstatic/pkg/';
 
   config.set({

tools/post_install.sh

@@ -10,4 +10,4 @@ then
 fi
 
 echo "Creating a tox env which will contain xStatic libraries, horizon, and openstack_dashboard"
-tox -epy36 --notest
+tox -epy38 --notest