logparse: ignore a line

Setting up exim4-config (4.93-9) ...
Adding system-user for exim (v4)

2020-01-17 17:28:04 Warning: No server certificate defined; will use a selfsigned one.
 Suggested action: either install a certificate or change tls_advertise_hosts option

Signed-off-by: Mattia Rizzolo <mattia@debian.org>