Ticket 47968 - RFE send logs to journald
    
    Bug Description:  Instead of writing the debug logs directly to the
    disk, it is possible to send them to journald, on platforms where
    journald is available.
    
    Fix Description:
    * This patch enables a configuration for selecting log
    backends, and defines the basic wrappers to route log entries
    based on the backend selection. The backends for syslog and
    journald have had identities reserved.
    * This enables the configure option --with-systemd
    which will allow us to link to the daemon and journald apis from
    within slapd.
    * Allows all backends to log simultaneously. Configuration is a
    comma seperated set of values taking "dirsrv-log,syslog,journald'.
    Unknown values are ignored, invalid is ignored. At least one valid
    log backend must be in the list.
    
    https://fedorahosted.org/389/ticket/47968
    
    Author: wibrown
    
    Review by: mreynolds (Thanks!)