csrgen: support openssl 1.0 and 1.1
    
    Support both openssl 1.0 and 1.1 APIs where sk_* functions got prefixed
    with OPENSSL_ in the latter version.
    
    Since referencing a symbol from a dynamically loaded library generates
    exception, use the AttributeError exception to catch it and fall back to
    the older method.
    
    Fixes https://pagure.io/freeipa/issue/7110
    
    Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>