caches: use individual namespaces per user to prevent beaker caching problems. - especially for mysql in case large number of data in caches there could be critical errors storing cache, and thus preventing users from authentication. This is caused by the fact that we used single namespace for ALL users. It means it grew as number of users grew reaching mysql single column limit. This changes the behaviour and now we use namespace per-user it means that each user-id will have it's own cache namespace fragmenting maximum column data to a single user cache. Which we should never reach.