Permission to read all tasks is given to high-level admins.
Managed permission for automember tasks is given to automember task admins.
"targetattr=*" is used because tasks are extensibleObject with
attributes that aren't in the schema.
Part of the work for: https://fedorahosted.org/freeipa/ticket/3566
Reviewed-By: Martin Kosek <mkosek@redhat.com>