Add host-specific Telegraf configuration

Rosetta uses the filestat plugin to report when scripty and other batch
processes run, and Silk uses the apache plugin to report scoreboard info.

It's *horrible* to have "if hostname = foo" in the template file.
But the previous status is even worse: local changes to the config file in
the servers, missing from the ansible repo, risking that a playbook run
will overwrite them if I'm not careful to skip those hosts.