Comment 6 for bug 1190986

As a workaround I added a cronjob to clean the table every 5 min:
*/5 * * * * su -c 'psql -d maasdb -c "DELETE FROM piston_nonce WHERE id < (SELECT max(id)-1000 FROM piston_nonce);"' postgres >> /var/log/maas/nonce_cron.log
Since there is no timestamp in the table I keep the last 1k entries.