allow this puppet module to manage debian/redhat repos

I copied this code from the other puppet module for logstash-forwarder at https://github.com/elasticsearch/puppet-logstashforwarder

If you add "manage_repo => true" to the class declaration, it will attempt to install a package from elastisearch for your via apt-get or redhat.

Disclaimer: I didn't test this super-thoroughly but it's been running well on the few tests I ran.  It's also been a part of the other logstashforwarder git repository for a while now, so in theory it's already well tested.