duh

This is required if the graylog web ui is run behind a reverse proxy,
such as in this role!

This is a bit of a hack. The mongodb service restarts successfully,
but it's not ready straight away to receive commands straight away.
So just wait a second, then issue the set compatibility command.

No need for list when there's just 1 handler

graylog listens on localhost port 9000, so put nginx in front of it
so we get something safe and stable listening on port 80 to save
graylog itself running as root to listen on a privileged port