statsd module: provision Ganglia backend support

StatsD logs to Graphite by default, but it has a pluggable architecture
that allows for additional backends to be configured by placing a JavaScript
module in a special file path. This patch adds a Ganglia backend and instructs
Puppet to deploy it to the backend module directory. I'm not going with
git-deploy because I don't expect to be revising it continuously. My plan is to
be satisfied that the implementation is stable after running it for a while and
then move the code to our repo / package.

Change-Id: I79f0d05c59cb7715df413940a13aaf55e8787a94