'Determine NAS security option setting when \'auto\' is assigned.
This method determines the final \'true\'/\'false\' setting of an NAS
security option when the default value of \'auto\' has been detected.
If the nas option isn\'t \'auto\' then its current value is used.
:param nas_option: The NAS security option value loaded from config.
:param mount_point: Mount where indicator file is written.
:param is_new_cinder_install: boolean for new Cinder installation.
:return string: \'true\' or \'false\' for new option setting.'

def _determine_nas_security_option_setting(self, nas_option, mount_point, is_new_cinder_install):

    if (nas_option == 'auto'):
        file_name = '.cinderSecureEnvIndicator'
        file_path = os.path.join(mount_point, file_name)
        if os.path.isfile(file_path):
            nas_option = 'true'
            LOG.info('Cinder    secure    environment    indicator    file    exists.')
        elif is_new_cinder_install:
            nas_option = 'true'
            try:
                with open(file_path, 'w') as fh:
                    fh.write('Detector    file    for    Cinder    secure    environment    usage.\n')
                    fh.write('Do    not    delete    this    file.\n')
                self._execute('chmod', '640', file_path, run_as_root=self._execute_as_root)
                LOG.info('New    Cinder    secure    environment    indicator    file    created    at    path    %s.', file_path)
            except IOError as err:
                LOG.error('Failed    to    created    Cinder    secure    environment    indicator    file:    %s', err)
        else:
            nas_option = 'false'
    return nas_option
