touch up final test condition (#1338)

The action used to fail a few times at the end as it wasn't aware of
what the end state should look like.
With having an `assert` block, it should now be able to judge more
accurately.

testdriver/onboarding.yml

@@ -10,3 +10,5 @@ steps:
         text: Get Started
         description: button to complete onboarding
         action: click
+      - command: assert
+        expect: the cpu usage graph is being displayed