python: always assign best_score after train

[henry0312]

This commit will regain backward compatibility that has been broken
after 015c8ff.
When not using early_stopping, best_score has scores calculated with all trees.

I'm sorry that I overlooked #870 (comment).

[henry0312]

@wxchan @StrikerRUS

[guolinke]

The travis test on OSX often met time-out error. Can we solve it ?

[henry0312]

The travis test on OSX often met time-out error.

This is mostly because Travis has lack of OS X instances... 😢

[StrikerRUS]

Yeah, this is sad, but I think we cannot do anything with it (only reduce number of tests on OSX) 😞

[Laurae2]

@guolinke To avoid timeout, can we run several tests in parallel?

[StrikerRUS]

@guolinke @henry0312 @Laurae2 Can we somehow benefit from caching on OSX?

[guolinke]

@StrikerRUS yeah, most time of OSX test are used on package installation.

[StrikerRUS]

@guolinke Unfortunately, I have little knowledge of *nix systems, so, probably I'll not be able to do it without your help.

btw, maybe it's better to create a separate issue for Travis speedup?

[StrikerRUS]

As I understand, we should cache the folder (which one?) with installed packages and at the beginning of build check these packages are already installed.
Like this one, but for Travis:
https://github.com/tunnelvisionlabs/NOpenCL/blob/master/appveyor.yml#L18
https://github.com/tunnelvisionlabs/NOpenCL/blob/master/build/appveyor-install.ps1

[StrikerRUS]

According to the latest PR, instance just clones git repo and connection to it is lost:
https://travis-ci.org/Microsoft/LightGBM/jobs/272489939

I remember cases when instance even cannot be started at all.

So, all our tricks with cache will not be launched...

[guolinke]

@StrikerRUS I think it freezes.
@wxchan @henry0312 Is that the bug of OSX ?

[henry0312]

I don't know, but it seems a problem of Travis.

[StrikerRUS]

@guolinke @henry0312
https://www.traviscistatus.com/incidents/2f0443bbphld