The same change has been made in the live ISO test, so keep this change uniform
also in the test_repos_sanity.sh test and vm.install script.
Related: rhbz#1828808
It's not possible anymore to use latest-RHEL-$major in the URLs, it's necessary
to also supply the minor version for rel-eng composes. Also the URL structure
had to be updated due to changes on the download servers.
Related: rhbz#1828808
