IPA: Change the default of ldap_user_certificate to userCertificate;binary
    
    This is safe from ldb point of view, because ldb gurantees the data is
    NULL-terminated. We must be careful before we save the data, though.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2742
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>