First attempt at logstash

This is a first attempt to add logstash. It does so by connecting
machines in the topology:

 * node1.internal rsyslog daemon, transports to
 * logging.internal rsyslog daemon, transports to
 * logging.internal logstash daemon

However there is something funny in the config where local messages on
logging.internal are transported to logstash, and remote messages from
node1.internal are saved to disk by logging.internal rsyslog, but
node1.internal messages aren't then being delivered to logstash.

This commit is mainly to save the work that I had.
Syslog directly to central logstash server

This commit removes the central syslog server daemon on
logging.internal:514 and has each syslog client log directly to
logstash on logging.internal:5544.

There's still an ongoing issue of _grokparsefailure tags showing that
logstash isn't happy with the syslog format. Will investigate next.