Parse and report on rabbitmq logs.

While we're looking for errors to report we may as well report metrics of how
many of each log level we're seeing in the logs.
Only count log messages in the latest interval
Add missing status OK
Refactor elasticsearch plugin and rabbitmq_logs

Use elasticsearch to look for rabbitmq log errors and warnings
Allow the user to specify a host and port for elasticsearch
Merge pull request #34 from rcbops/rabbit-logs

Rabbit logs