batcave: adjust ssh_known_hosts so buildvm-s390x-01.stg works
    
    For ages buildvm-s390x-01.stg.s390.fedoraproject.org has needed it's ssh
    key accepted on ansible runs. The problem was we were not extending the
    cert authority to handle this subdomain. This commit fixes that.
    
    Signed-off-by: Kevin Fenzi <kevin@scrye.com>