ARROW-217: Fix Travis w.r.t conda 4.1.0 changes

[xhochy]

Travis is happy, fixes the problems we see with Travis in #85

[xhochy]

For reference, after the conda config --add channels calls.

conda info -a some days ago:

         channel URLs : https://conda.anaconda.org/apache/osx-64/
                        https://conda.anaconda.org/apache/noarch/
                        https://conda.anaconda.org/conda-forge/osx-64/
                        https://conda.anaconda.org/conda-forge/noarch/
                        https://repo.continuum.io/pkgs/free/osx-64/
                        https://repo.continuum.io/pkgs/free/noarch/
                        https://repo.continuum.io/pkgs/pro/osx-64/
                        https://repo.continuum.io/pkgs/pro/noarch/

now:

         channel URLs : https://conda.anaconda.org/apache/osx-64/
                        https://conda.anaconda.org/apache/noarch/
                        https://conda.anaconda.org/conda-forge/osx-64/
                        https://conda.anaconda.org/conda-forge/noarch/

i.e. continuum's channels are missing. Those were listed before we added the channels.

[wesm]

+1, thank you

[wesm]

@kalefranz can you or someone on the conda team comment on what may have changed with the channel URLs? thank you =)

[kalefranz]

In 4.1.0 we introduced a bug where defaults wasn't automatically added to channels in ~/.condarc if the file already existed.

We've fixed it here: conda/conda#2670
4.1.1 will be released with that fix and others in a few hours

In general, as of 4.1.0, channel order now matters. Before, all channels were thrown together and the package with the highest version comparison won. Now, if a package exists in a higher priority channel (i.e. the channel comes first in the channel list), then that package wins.

We'll continue to refine and improve on channel/package priority. This is just a first step.

[wesm]

@kalefranz thank you for the quick reply. Per the channel priority, am I correct that the last channel added has the highest priority? (so in our case, apache channel would supercede conda-forge?)

[kalefranz]

Yes, the last channel added with conda config ends up being the first channel in the channels list in ~/.condarc, and thus has the highest priority.

[kalefranz]

FYI we're also adding a auto_update_conda option that defaults to true, but that can be set to false to disable conda's aggressive self-update. Definitely useful in some CI situations. That'll be in both 4.1.1 and 4.0.9 coming out later today.