Ticket #47693 - Environment variables are not passed when DS is started via service
    
    Description: Environment variables (except TERM and LANG) are ignored
    if a program is started via service.
    
    If it is started with systemctl, it takes this COMMAND and the values
    are correctly passed to the server.
    systemctl set-environment SLAPD_MXFAST=0 MALLOC_TRIM_THRESHOLD_=4096
    
    To control them explicitly and to provide the same instructions to
    the service and systemctl, it'd be good to have some variables
    (SLAPD_MXFAST, MALLOC_TRIM_THRESHOLD_ and MALLOC_MMAP_THRESHOLD_ in
    this patch) configurable.
    
    https://fedorahosted.org/389/ticket/47693
    
    Reviewed by rmeggins@redhat.com (Thank you, Rich!!)
    (cherry picked from commit 02169effb14ea082cdfed5377244b4ffedb7c437)
    (cherry picked from commit 476a1930ab5cbe2fbee9f94586c000980089ebf2)
    (cherry picked from commit ae2e7f4d277a608e8c2a893f15eb9b4c397284cc)