Correct path to HTTPD's systemd service directory
    
    Ticket #5681 and commit 586fee293f42388510fa5436af19460bbe1fdec5 changed
    the location of the ipa.conf for Apache HTTPD. The variables
    SYSTEMD_SYSTEM_HTTPD_D_DIR and SYSTEMD_SYSTEM_HTTPD_IPA_CONF point to
    the wrong directory /etc/systemd/system/httpd.d/. The path is corrected
    to  /etc/systemd/system/httpd.service.d/.
    
    https://fedorahosted.org/freeipa/ticket/6158
    https://bugzilla.redhat.com/show_bug.cgi?id=1362537
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Abhijeet Kasurde <akasurde@redhat.com>