add ability to manage default file* service parameters

  * /etc/(default|sysconfig/elasticsearch
Lint file init.pp
moved default service file resource in elasticsearch::service

Those settings are more related to the service itself. The class
elasticsearch::config is focused on intrinsic behaviour of ES
use notify instead of subscribe
add 2 tests related to the management of /etc/(default|sysconfig)/elasticsearch
Merge pull request #21 from mbornoz/default-settings

add ability to manage default file* service parameters