branchcache: use update_disk to refresh 'served' and 'served.hidden'...
branchcache: use update_disk to refresh 'served' and 'served.hidden'
The `update_disk` method is dedicated to this kind of usecase. Now that the writting patterns are more consistent, we can use it to warm these two important cache.
I am dropping the first comment about "refreshing all the others" because it is
false. If a branchmap already exist for "served", none of the subset will be
updated.