Certificate issues with github in Python 2

[fmassa]

Tests in Python2 are now failing with error

IOError: [Errno socket error] [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:727)

see e.g., https://travis-ci.org/pytorch/vision/jobs/573261632

This is due to a change in github it seems, and has been worked around in PyTorch in pytorch/pytorch#25042

A few possible solutions:

• change the download link in the test to use a different domain than github
• skip the test for Python2 for now
• use the unverified context trick from Temporarily fix hub SSL cert issue pytorch#25042, but this can lead to some vulnerabilities

I'd vote for trying out option 2 for now.

[kimishpatel]

@fmassa, it seems to be an issue on some of the py3 builds also (pytorch_linux_xenial_cuda9_cudnn7_py3_NO_AVX2_test , pytorch_linux_xenial_cuda9_cudnn7_py3_NO_AVX_NO_AVX2_test). Any suggestions?

[fmassa]

@kimishpatel those seem like PyTorch builds? I think they relate to torchhub, and maybe not torchhub? Could you point to those issues?
cc @ailzhang