Code review comment for ~hloeung/charm-rsyslog-forwarder-ha:master

First of all, sorry about the delay in replying here.

Logging to these log files are not enabled by default in Ubuntu.

I still need to investigate why the `rsyslog` daemon is failing when
these are enabled but the files don't exist. It's likely AppArmor.

I'm going to update this MP to check if these files exist on disk and
only enable logging to these if they do.