Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Centralized all LDAP config logic in to Gitlab::LDAP::Config. We had varying configuration for devise/omniauth and other things. For example, user_filter was never taken in to account for devise/omniauth so a user object would always be created, even if the user did not match the user_filter.
Fixes gitlab-org/gitlab-ce#21195, https://gitlab.com/gitlab-org/gitlab-ce/issues/15396 and gitlab-org/gitlab-ce#13296
master (if you do - rebase it please)