Remove SimpleTestTest dependency on the node frontpage

Part of #1811016: [meta] Decouple tests from Node module. From the VDC sandbox.

To test that assertTitle() and assertNoTitle() work as expected, SimpleTestTest visits node and checks the title pattern. Remove this dependency by checking user instead. (We still specify the path explicitly since we are looking for a specific title pattern.)

Bonus: Remove a couple of vague assertion messages in the process.