Pass in URL path to use when calling wait_for_http_request or allow_for_http_request

Previously, the URL path to expose on the Webrick server as the endpoint was the same as the local file path.  This caused problems in the Windows side where the file path was something like "D:\dirname\file.cfg" because it contains invalid characters for a URL.  

The change here changes the above two methods to explicitly take in a URL path to use as the endpoint.  The calling code uses the "to_slug" gem to clean up invalid characters when generating the URL prior to passing it to the above two functions.