SYSDB: Add new funtions into sysdb_sudo
    
    This patch adds two new functions into public
    API of sysdb_sudo:
    * sysdb_search_sudo_rules
    * sysdb_set_sudo_rule_attr
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2081
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>