mxservicectl: Accept service unit name in mxstartups

Regard the 4th column of /etc/mxstartups as the name of a systemd
service unit if it ends in ".service".  In that case, ignore the
username and use systemctl to start/stop that unit.

The idea is to use /etc/mxstartups for services, which we want to run as
a systems service, e.g. to use the features of systemd. Currently there
is an option to use unit files with an encoded hostname but we prefer to
have the information of which hosts starts which service in
/etc/mxstartups.

mxservicectl

@@ -19,7 +19,14 @@ function mxsrv_start_one() {
 
    . ${cfg}
 
-   su - ${MX_SRV_USER} -c "${MX_SRV_SCRIPT} start" &
+   case "${MX_SRV_SCRIPT}" in
+       *.service)
+           systemctl start "${MX_SRV_SCRIPT}"
+           ;;
+       *)
+           su - ${MX_SRV_USER} -c "${MX_SRV_SCRIPT} start" &
+           ;;
+   esac
 
    mv ${cfg}{,.r}
 
@@ -34,7 +41,14 @@ function mxsrv_stop_one() {
 
    . ${cfg}
 
-   su - ${MX_SRV_USER} -c "${MX_SRV_SCRIPT} stop" &
+   case "${MX_SRV_SCRIPT}" in
+       *.service)
+           systemctl stop "${MX_SRV_SCRIPT}"
+           ;;
+       *)
+           su - ${MX_SRV_USER} -c "${MX_SRV_SCRIPT} stop" &
+           ;;
+   esac
 
    rm ${cfg}