QA: Test that hidden post's content isn't visible

Test checked that "marked as hidden" but did not check that content of
hidden post is hidden.
Also enable these tests on beta and test2, not sure why they weren't.
Also remove bogus comment about User_talk.

Test will fail until bug 71132 is fixed; such fix should merge or be
based off this.

Change-Id: I83a93b1fed53aac6c36ff70edfcdbb0678760233