Need to consider robust test data like https://csrc.nist.gov/projects/pki-testing

[nick-mobilecoin]

Use the PKI test suite, https://csrc.nist.gov/projects/pki-testing, to verify the certificate chain logic

• Tests for 4.1.x of PKITS #73
• Convert PKITS tests to integration tests #75
• Tests for 4.2 of PKITS #76
• Add tests for section 4.3 of PKITS #78