Ubuntu: Use utf8mb3 charset in MySQL

... to fix the broken idempotency in litmus job. Current mysql/mariadb
in Ubuntu replaces utf8 with uft8mb3 automatically and this behavior
results in unexpected change in second run.

Related-Bug: #1929073
Change-Id: Ide1f9484d0f9aaf719ccfbe3ab5282ecd901ae6b

spec/acceptance/mysql_spec.rb

@@ -10,7 +10,13 @@ describe 'openstacklib mysql' do
 
       class { 'mysql::server': }
 
-      ::openstacklib::db::mysql { 'ci':
+      $charset = $::operatingsystem ? {
+        'Ubuntu' => 'utf8mb3',
+        default  => 'utf8',
+      }
+
+      openstacklib::db::mysql { 'ci':
+        charset       => $charset,
         password_hash => mysql::password('keystone'),
         allowed_hosts => '127.0.0.1',
       }