Use case dataset download fails on Windows with CERTIFICATE_VERIFY_FAILED #2676

Description

On a clean Windows machine running 6.8.0 RC1, RunUseCase.py can't download use case data:

> & 'C:\Program Files\ShapeWorks\bin\swpython.bat' .\RunUseCase.py deep_ssm --tiny_test
Step 1. Acquire Data
Downloading deep_ssm_femur_tiny_test from https://www.sci.utah.edu/~shapeworks/data-sets/use-case-data/deep_ssm_femur_tiny_test-v1.zip
...
RuntimeError: Could not reach https://www.sci.utah.edu/~shapeworks/data-sets/use-case-data/deep_ssm_femur_tiny_test-v1.zip
  <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1000)>

Cause

The certificate chain for www.sci.utah.edu ends at the emSign Root CA - G1 root. A fresh Windows install ships with only a small set of roots and downloads the rest on demand, but only when Windows itself verifies a connection (for example, in a browser). Python verifies through OpenSSL, which reads the Windows root store as it stands, so it doesn't find the root.

This explains why it works on some machines and not others: visiting the site once in Edge installs the root.

Fix

Have shapeworks/datasets.py verify against certifi's root bundle as well as the system roots. certifi is already in python_requirements.txt and bundled with the install. The fix goes to master first. release_v6.8.0 also needs it; it will come over with the other master fixes being merged into 6.8.

Workaround

Open the dataset URL once in Edge, or set SSL_CERT_FILE to the path of certifi's cacert.pem in the ShapeWorks Python install.