Fix 'The "Tails documentation" link on the Desktop works' scenario.

The TailsOfflineDocHomepage.png image doesn't match what we see any
more (I have no clue why), so let's use Dogtail and solve this once
and for all, hopefully.

features/torified_browsing.feature

@@ -106,7 +106,7 @@ Feature: Browsing the web using the Tor Browser
     Given I have started Tails from DVD and logged in and the network is connected
     When I double-click on the "Tails documentation" link on the Desktop
     Then the Tor Browser has started
-    And I see "TailsOfflineDocHomepage.png" after at most 10 seconds
+    And "Tails - Getting started..." has loaded in the Tor Browser
 
   Scenario: The Tor Browser uses TBB's shared libraries
     Given I have started Tails from DVD and logged in and the network is connected