Ticket 3 - headers contain ifdef blocks that should be removed.
    
    Bug Description:  Using ifdef with_systemd in the header is not very clean
    as it adds a dependency on clients to know about this.
    
    Fix Description:  Move the ifdef into the systemd functions. The ifdef was
    changed to HAVE_SYSTEMD. If not HAVE_SYSTEMD, functions return an error 10,
    SVRCORE_MissingFeature, to indicate the feature was not compiled correctly.
    
    https://pagure.io/svrcore/issue/3
    
    Author: wibrown
    
    Review by: nhosoi (Thanks!)