[WiP] RSpec improvements and upgrade to RSpec 3.0

This is a working progress PR, initially started with the motivation in mind to provide clarity to the LogStash tests and to upgrade them to 3.0

This is an WiP PR, that is mainly open so we can reach a common point on how do we want to have our test looking like. 

If you have any question or doubt about why something is like it is, fire a comment :smile: 

- purbon
I agree, it is difficult to reason the tests with the config so far removed. I also do not see how we can use factories to remedy this without overcomplicating the problem. Without a clean and supported config API to help with building of a config for testing, I'd prefer leaving the config file-fixtures over creating supporting factory classes. That being said, I have no problem with leaving the config strings in-place :). Though, I understand the desire to clean that up. I am also OK with the file fixtures. It is not too hard to go into a file and see what is being checked.