Fix ossec dependency

added back installing mailutils.

The task file `install_files/ansible-base/roles/ossec_server/tasks/mon_configure_ossec_gpg_alerts.yml` installs the ossec server package.

The task file `install_files/ansible-base/roles/ossec_server/tasks/mon_install_postfix.yml` install postfix and its dependencies.

The rest of the ossec dependencies are listed in the OSSEC DEBIAN/control file. `install_files/ossec-server/DEBIAN/control`