Update.php fails to flush css/js if aggregation is enabled

Problem/Motivation

If update.php runs the _drupal_flush_css_js(); is called. This set's a new css_js_query_string, but this does NOT cause a regeneration of CSS and JS files if aggregation has been enabled.

If a module is updated and adds new CSS selectors or has large CSS and JS changes these files need to be updated. We had such a failure in #2432917: Upgrading breaks menu

Proposed resolution

Also regenerate the CSS and JS files.

Remaining tasks

User interface changes

None

API changes

None