More htpasswd fallout: use httpd-tools
    
    Newer buildah tests now depend on encryption functionality
    only present in later (2.7? 2.8?) versions of docker.io/registry.
    So, undo our earlier change in which we forced registry:2.6
    to use its htpasswd. Instead, tests now require httpd-tools
    package and we use native host htpasswd. We revert back to
    using registry:2 (no dot), which is a moving target, so be
    prepared for future breakage.
    
    Signed-off-by: Ed Santiago <santiago@redhat.com>