require chef/resource as we are working with some resources here.
lookup_loadstash_resource will find items in the resource collection.

logstash_clean_configs will remove any configuration files that are not
in the resource collection. This could be a race condition, certainly
something to be aware of with execution order.

logstash_delete_old_config will create a file resource for specified
files and then delete them.

lookup_logstash_confdir lookups a resource and returns its conf_dir
attribute.