Prevent deadlock on variable table when clearing cache

When clearing cache we see deadlocks on the variable table, most are due to this vset that get needlessly called 15 times.

Variable contents:
```
os_search_solr_display_mode: Array
(
    [browse_blog] => teaser
    [browse_book] => teaser
    [browse_class] => teaser
    [browse_event] => teaser
    [browse_faq] => teaser
    [browse_media_gallery] => teaser
    [browse_link] => teaser
    [browse_news] => teaser
    [browse_page] => teaser
    [browse_presentation] => teaser
    [browse_person] => teaser
    [browse_software_project] => teaser
    [browse_software_release] => teaser
    [browse_harvard_course] => teaser
    [browse_biblio] => teaser
)
```