As part of our zuulv3 effort, we want to start testing statsd from
nodepool-launcher. Expose the ability to prefix our requests, as not
to affect production data.
Change-Id: I943df7789cfa6c69f5c5d360c9b80af6328ca878
Depends-On: I8bef6aae5a566ff3a34e816ece14f9cfc1ef289d
Signed-off-by: Paul Belanger <pabelanger@redhat.com>