Ubuntu 14.04 sets logs in ``/var/log/audit`` to mode ``0400`` by default,
which makes sense because only the root user should be able to view the
logs. No users should ever be adjusting or editing the audit logs.

The STIG requirement states that log files must have mode ``0640`` or less.
The Ansible tasks in this role will set the mode to ``0400`` to match
Ubuntu's default.