asset-check: report to Graphite rather than Ganglia

Ganglia was always a poor fit for this sort of metric data, but the Graphite
setup on professor was moribund and I did not want to encumber it with
additional dependencies. But now that Graphite is on tungsten, metric data
should be reported to Graphite instead.

Bug: 60193
Change-Id: I1b6771b807215840d54424dee24957962e16ebef