GA Virtual pageview on Webform reload: is there an easier way?
An easier method (that requires no coding) would be to set the webform's "Redirection location" setting to "Custom URL" and enter 'node/%nid?f=my_webform_success'.

This will post the form to itself and also allow you to add some unique key/value to the URL.

Then within Google Analytics you can set a Goal with the Goal URL set to 'f=my_webform_success' and the Match Type set to "Regular Expression Match".