Fix CSS classes used by UI tests

plugins/Installation/FormDatabaseSetup.php

@@ -73,7 +73,7 @@ class FormDatabaseSetup extends QuickForm2
             ->loadOptions($adapters)
             ->addRule('required', Piwik::translate('General_Required', Piwik::translate('Installation_DatabaseSetupAdapter')));
 
-        $this->addElement('submit', 'submit', array('value' => Piwik::translate('General_Next') . ' »', 'class' => 'btn btn-lg'));
+        $this->addElement('submit', 'submit', array('value' => Piwik::translate('General_Next') . ' »', 'class' => 'submit btn btn-lg'));
 
         // default values
         $this->addDataSource(new HTML_QuickForm2_DataSource_Array(array(

plugins/Installation/FormFirstWebsiteSetup.php

@@ -61,7 +61,7 @@ class FormFirstWebsiteSetup extends QuickForm2
                                1 => Piwik::translate('SitesManager_EnableEcommerce'),
                           ));
 
-        $this->addElement('submit', 'submit', array('value' => Piwik::translate('General_Next') . ' »', 'class' => 'btn btn-lg'));
+        $this->addElement('submit', 'submit', array('value' => Piwik::translate('General_Next') . ' »', 'class' => 'submit btn btn-lg'));
 
         // default values
         $this->addDataSource(new HTML_QuickForm2_DataSource_Array(array(

plugins/Installation/FormSuperUser.php

@@ -65,7 +65,7 @@ class FormSuperUser extends QuickForm2
                     ),
             ));
 
-        $this->addElement('submit', 'submit', array('value' => Piwik::translate('General_Next') . ' »', 'class' => 'btn btn-lg'));
+        $this->addElement('submit', 'submit', array('value' => Piwik::translate('General_Next') . ' »', 'class' => 'submit btn btn-lg'));
 
         // default values
         $this->addDataSource(new HTML_QuickForm2_DataSource_Array(array(