* Make number of threads configurable
* Improve naming
* Update path and log options for Logstash 2.4
* Use the correct logs directory

Partially-Implements: blueprint monasca-roles
Change-Id: I09388de4d31740f2786393c957201bd037572226

This is a Logstash component which reads processed logs from Kafka
and writes them to Elasticsearch (or some other backend supported by
Logstash).

Ingesting the logs from this service with Fluentd will be covered under
a different commit.

Change-Id: I2d722991ab2072c54c4715507b19a4c9279f921b
Partially-Implements: blueprint monasca-roles