Omit combustion module in initrds for already configured systems

If the initrd is hostonly and /etc/machine-id already exists, don't include
the combustion dracut module and its dependencies.

module-setup.sh

@@ -1,5 +1,9 @@
 check() {
-	return 255
+	# Omit if building for this already configured system
+	if [[ $hostonly ]] && [ -e /etc/machine-id ]; then
+		return 255
+	fi
+	return 0
 }
 
 depends() {