This adds a varnish layout with a single graph for monitoring cache hits
vs. misses. The varnish plugin in Telegraf is able to collect far more
statistics on Varnish (complete list:
https://github.com/influxdata/telegraf/tree/master/plugins/inputs/varnish).
However, by default only hits, misses, and uptime are present in the
configuration. We don't currently have a way for a layout to inspect the
fields present for a particular measurement for it to decide which cells
to show, so this will be necessary if we wish to add monitoring for
things like ESI errors, backend connects, memory stats, threads, etc.
Peter A. Bigot
Chris Goller
Tim Raymond