Something (?) changed which is causing ssh-keyscan to try to use
IPv6 lo on our test nodes which does not work. Use ssh-keyscan -4
to work around this.
There is no user impact since we expect the user to interactively
accept the keys in the tutorial.
Change-Id: Ibf033de7a3ed6cb41993c6f4adbddeeb53f4c09c