Try use old way of setting page load timeout if new way fails. Fixes S…

…eleniumHQ#3654

The release version of Firefox doesnt have the latest W3C setPageTimeout
algorithm. If the W3C version fails, try the old way.

py/selenium/webdriver/remote/webdriver.py

@@ -722,10 +722,10 @@ def set_page_load_timeout(self, time_to_wait):
         :Usage:
             driver.set_page_load_timeout(30)
         """
-        if self.w3c:
+        try:
           self.execute(Command.SET_TIMEOUTS, {
               'pageLoad': int(float(time_to_wait) * 1000)})
-        else:
+        except WebDriverException:
           self.execute(Command.SET_TIMEOUTS, {
               'ms': float(time_to_wait) * 1000,
               'type': 'page load'})