WIP: Fix redis details
Created by: bbodenmiller
As discussed at https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/224 and add5d43b the redis setup details aren't quite correct.
Currently the upgrade and installation guides differ in how you should set socket permissions. This PR aims to unify the settings both for a few old upgrade guides and, for users with already broken installations, in a new upgrade guide.
I will squash and make this mergeable if other users agree.
/cc @axilleas @hobarrera