Pull poll out of icinga and into util

We are going to need poll for the new sensu service so it would make
sense to pull it out into a shared namespace
Add Sensu Service and pass http config through

In the options map for a service in config.yml you can now pass through
a map with key http which will be passed through as the options to the
httpkit client (options here: http://http-kit.org/client.html#options)
Refactor services to share polling code