Bug 1405325 - Fix webdriver.transport.HTTPWireProtocol#url. r=maja_zf

The self.path_prefix attribute does not exist.  It should be
self.url_prefix.

MozReview-Commit-ID: 8LGES8GsTsm

--HG--
extra : rebase_source : a59f92070a6f35acda166836528704d03248c48c

testing/web-platform/tests/tools/webdriver/webdriver/transport.py

@@ -63,7 +63,7 @@ class HTTPWireProtocol(object):
         self._timeout = timeout
 
     def url(self, suffix):
-        return urlparse.urljoin(self.path_prefix, suffix)
+        return urlparse.urljoin(self.url_prefix, suffix)
 
     def send(self, method, url, body=None, headers=None):
         """Send a command to the remote.