We check whether we can access the certificate files shipped with convert2rhel prior to installing them. The check for the directory they live in was checking whether the directory was readable and writable. We don't write to that directory, though, so the check shuld be whether the directory is readable and executable.

Note that convert2rhel should always be run by root this bug won't be encountered in normal use. I encountered it when the unit_tests were run as a user who didn't have write permission to the git checkout.

Acceptance Criteria:

Change the owner and group of convert2rhel/data/8/x86_64/rhel-certs to root:root. Change the mode to 0755. As a non-root user, use pytest convert2rhel/unit_tests/cert_tests.py to run the integration tests for cert.py. Acceptance is if the unittests pass in this configuration. Failure is if the cert tests fail (currently 2 fail.when cert.SystemCert() is initialized (in _get_cert()