dtfscript: Use isup() in prestart() for services

.config/dtfscripts/common_service.sh

@@ -29,7 +29,7 @@ function svc_log() {
 
 # Basic pre-start checks. Stick extra checks in prestart-extra
 function prestart() {
-	if pgrep $service_process > /dev/null 2>&1; then
+	if isup; then
 		svc_log "Already running" 0
 		return 1
 	fi