Add all instances attributes to config templates

Fix for issue #333.
Passes all instance attributes into template variables allowing any instance attribute to be used with @attribute_name.
EX:
default['logstash']['instance']['server']['elasticsearch_ip'] = '10.10.10.10' can be called in the template with @elasticsearch_ip without having to set default['logstash']['instance']['server']['config_templates_variables'] = { 'elasticsearch_ip' => '10.10.10.10' }

The same fix can be applied to providers/plugins if necessary.