Roles and performance schema

performance_schema ignores roles. This is a feature request, but a new user would probably think this is a bug.

1) performance_schema.threads has a ROLE column, but it's always NULL.
2) When a user connects, a matching row is searched in performance_schema.setup_actors, including the ROLE column. However, the check is never re-done after connection, even if the user sets a role. In practice, a row with ROLE <> '%' will never match anything.