statsd/dogstatsd support for tracking consul template events

It would be really handy to have built in support for sending statsd/dogstatsd metrics on notable consul-template events. The most obvious of which being restarts. For statsd that'd probably be something like `consul-template..restart`, for dostatsd `consul-template.restart#template:identifier`. They may not currently be something obvious to use for identifier currently, perhaps the "flag" that enables stats would include that.

This originally occurred to us while trying to debug/track down https://github.com/hashicorp/consul/issues/2430 where it would have been really useful to be able to track which processes were being restarted when at a glance.

Originally brought up on the [list](https://groups.google.com/forum/#!msg/consul-tool/XTvu0xk3dJs/ad-fWvhIDQAJ) where @slackpad mentioned "I can think of some other situations where watching restarts could be useful, such as with quiescence timers." General/immediate solution suggested there was to use a wrapper around the restart command that emits the stats.