Return 4XX or 5XX status code on failure

[mestebangutierrez]

Up to now, whenever the service fails it returns a response with status code 200 and "false" as body.

When the service fails it should return a proper 4XX or 5XX status code depending on whether the failure is due to an incorrect client interaction or a problem within the service implementation.

[alejandrofcarrera]

This issue is fixed due to compatibility with Gitlab response.
Standard says something and people does other :)

[mestebangutierrez]

Ok.