There you can download the module : https://modules.processwire.com/modules/duplicator/
I was not aware of this module/topic and spend some time developing a module to backup, clone and move sites to a local folder or even GoogleDrive and Dropbox.
The idea begun when I read about this Wordpress's plugin. I was planning to add features like s/FTP, Amazon Cloud, deployment installer and others great features from Wordpress Duplicator and release it
That "/var/www" is the root path (within your filesystem) where your webserver places the content of your domains. This can only be changed when you point your server to some other folder.
I guess you are currently working with the release version (1.2.9) of Duplicator, right? That one expands the site files into a directory level below which needs to be moved manually during the install. Please try the V1.3.10 above which should solve this.
Btw, @flydev, do you plan to include the sug