CI: migrate to travis container infrastructure

[jreback]

http://docs.travis-ci.com/user/migrating-from-legacy/

trivial I think to remove the sudo. but prob have to change some stuff (as we
use some apt stuff)

currently we externally cache, so that would have to be figure out (at a later date is ok)

[bashtage]

I haven't seen any major improvements in testing speed when using this. I switched pandas-datareader to this and the build time dropped form 3 to 1.5, which is something for a small project.

In terms of buidl time, I don't think it woudl do much for pandas. However, if you get faster access to build servers then it could be worth it - the backlog of PRs can get pretty big at times.

[jreback]

@bashtage thanks for the fb.

I have actually been noticiing that travis seems to be building faster lately (on the old infrastructure).

I think main benefit is we could use the travis caching (as opposed to the only pyx build cache that we use from iron-cache).

[jreback]

Might be a good reference: libdynd/libdynd#481
also scipy recently changed.

[nparley]

It seems that the travis job 27_slow_nnet_LOCALE is having problems with the container-based infrastructure. Also travis is not detecting the use of sudo and is running in containers on my fork at least. Compare https://travis-ci.org/nparley/pandas/jobs/124695152 and https://travis-ci.org/nparley/pandas/jobs/124778492. I have created a PR to add sudo: required for the time being.