Forward syslog messages logged by the kernel about HHVM to fluorine

HHVM doesn't always manage to write a stacktrace when it segfaults, so forward
warnings from the kernel about HHVM getting killed or respawned to fluorine.
I tested the selector and confirmed it matched the following message:

Oct  2 04:23:22 vagrant: [3762297.322324] init: hhvm main process (10963) killed by SEGV signal
Oct  2 04:23:22 vagrant: [3762297.322335] init: hhvm main process ended, respawning

Change-Id: I955c2385ba9c9c4c3fbcc2754936c5f2d2c166da