This change makes it possible for users to set the `elastic_heap_size_default`
value. Before this change, the option was unreachable due to a series of facts
ganerated template values. The options `elastic_heap_size` or `logstash_heap_size`
have also been exposed giving deployers the ability to define service specific
heap sizes as needed.
Change-Id: Ida3a57fdcff388f8e4bb3f325b787205a6183970
Signed-off-by: Kevin Carter <kevin@cloudnull.com>