Allow all syslog data to be forwarded to aggregator - if syslog_aggregator.all is true.

I had previously done the same change as #271 to my own cf-release, but noticed that PR hadn't been pulled in due to inactivity. 

Re-submitting this myself as I'd love to have the ability to see all the logs in one place (including system logs).

This patch could be smaller if #310 is merged :)