Make the logstash integration testing a gem

The purpose of this PR is to setup the foundations to have the integration testing support for logstash as a gem, there is still some thing that have to be improved, but for now this is able to:

* Provide two commands after the gem installation (lsit-deps and lsit-suite), no lsit-run for now.
* If the config, input and suite definitions are in the same logstash place it just runs the test without problems.

NOTICE: This is mainly a port of what was there but as a gem, next steps are to make this more nice, include more test, reports, to make the config/input/suite easy, etc.. but for now you can start reviewing and merging if good enought
I agree its a WIP, but if we dont use it is still better to not install them. Faster `bundle install` and clear intent when looking at the dependencies.