You can leverage the Script service within foundation.
In the Script service you can use standard java code. You could write you own method to write to the file system using java.io.File object.
You could also use a setValue and use an xPath expression that sets the value of a variable to the value of "%hoSTH%Test". I'm not sure what "%hoSTH%Test" is suppose to return. Are you trying to get the name of the host machine in there?
The incorporate the value of that variable in your file name.