tests: better testing of loaded certificates Tests were failing on systems like RHEL 7 where loading the system certificates results in CA certs being reported to Python. We add a feature that detects when we're able to load *and detect* the loading of system certificates. We update the tests to cover the 3 scenarios: 1) system CAs are loadable and detected 2) system CAs are loadable but not detected 3) system CAs aren't loadable