automatically insert ip into asset/publish host when {{ip}} is seen

should we do an `if(PUBLISH_HOST)` check to see if this is a meaningful values? The foreach above sneaks it in as process.env[key], so passes over if it's not there, but we don't check for that here yet.
```
if(process.env.PUBLISH_HOST) {
  console.log("Using publishing host "+process.env.PUBLISH_HOST+".");
}
if(process.env.ASSET_HOST) {
  console.log("Using published asset host "+process.env.ASSET_HOST+".");
}
```
or the like?