Simplify the gathering of host information.

[gabrieldemarmiesse]

I proposed a simplified version of the host info gathering. With this, we'll have less code to maintain and it'll be easier to understand for futur contributors.

There is also no need for the dictionary used to gather infos to be exposed at the top level, since it's undocumented, I removed it.

[coveralls]

Coverage decreased (-0.03%) to 85.294% when pulling 979075e on gabrieldemarmiesse:simplify_info_gathering into a181df5 on IDSIA:master.

[Qwlouse]

Hmm, not sure about this. The idea behind the current implementation was to make it easy to customize host-info from the user-level. I.e. if you want some custom information captured, just decorate a function with @host_info_getter(name='custom') and its results will be added to host_info.

On the other hand I can see the advantages of reducing complexity, and your code is clearly much simpler and more maintainability.
@JarnoRFB: Opinions?

[JarnoRFB]

I wouldn't necessarily break the user facing API for an internal simplification. The functionality also seems to be documented here https://sacred.readthedocs.io/en/latest/collected_information.html#host-info. Unless we can find a way to simplify and keep the feature, I would leave it.

[gabrieldemarmiesse]

I didn't see it was a user facing API. My bad.