shared/logs-show: show audit logs in blue

shared/logs-show: show audit logs in blue

Audit logs always have _TRANSPORT=audit and no PRIORITY= field set.  This means
that they are shown in the default foreground color. There can be quite a lot
of them, and they often repeat the same information that is already logged by
applications, leading to a "wall of text" effect. Let's mark them with a
different color. This splits the logs visually into "normal logs" and "audit
logs".