add support for the zookeeper plugin
add support for hdfs integration
changes per review:

* `supports` python vs. `depends`
* `include_recipe "python"` vs. install packages
* add comments for hdfs instances format
ignore the FC rule for this particular condition

Since we wish to allow users to make the best choices, leaving some of
the external Chef requirements up to the user to handle instead of
mandating that they use a particular version of a dependency cookbook.

This was further discussed in DataDog/chef-datadog#77
change supports to suggests for operator view
update changelog for hdfs contribution [ci skip]
Merge branch 'zookeeper' of https://github.com/Shopify/chef-datadog into Shopify-zookeeper
update changelog for zk constribution [ci skip]
Add legacy integration support
add options for statsd_forward_host and _port:

* this prevents clobbering of these options when
  using the beta agent in production
bump version for cooker