snippets/base_script.sh: add check if systemd is supported

snippets/base_script.sh

@@ -196,6 +196,16 @@ else
    terminal=false
 fi
 
+# -Is systemd supported on this system?
+# -
+systemd_supported=false
+systemd=$(which systemd)
+systemctl=$(which systemctl)
+
+if [[ -n "$systemd" ]] && [[ -n "$systemctl" ]] ; then
+   systemd_supported=true
+fi
+
 # - Print help?
 # -
 if [[ "$(trim $*)" = "-h" ]] || [[ "$(trim $*)" = "--help" ]] ; then