Unify generator

[ruflin]

• Use one script create generic beat or metricbeat
• Rename generate directory to template (UPDATE: generator)
• Share most parts of the testing makefile
• Update docs to new logic
• Update travis build file

[monicasarbu]

LGTM. Only a small comment about the name of the directory template, not to be confused with something else.

[monicasarbu]

@ruflin What about moving the scripts/generate.py script to the template directory to be together with the Beat templates, and rename the template directory to generator?

[ruflin]

@monicasarbu I actually just did the opposite step with this PR :-) The reason I put it under script (besides that it is a script) is that I think it is unlikely that we will change the name of the folder or move the folder in the near future. This means we will not break the generator again. All the other directories (be it template or generator or xyz) do not matter to the user as it we only have to adjust it inside the script. So I think we should keep script/generate.py but I have no strong opinion about the naming of the directory. Let me know what you prefer there.

[monicasarbu]

@ruflin That's a good point. I would say to keep the script in the script directory, and rename the directory with the templates to generator even if it contains only the templates as you will use the script anyway to generate the templates.

[ruflin]

@monicasarbu renamed

[monicasarbu]

Waiting for green