test: cert: Reflect change in behavior in tests
    
    Command cert-find with parameter sizelimit set to 0 no longer returns 0
    certificates but returns all.
    
    More precise ConversionError is returned when parameter is not
    convertible to its type.
    
    https://fedorahosted.org/freeipa/ticket/5381
    https://fedorahosted.org/freeipa/ticket/4739
    
    Reviewed-By: Petr Spacek <pspacek@redhat.com>