It turns out bionic ssh-keygen doesn't have the "-D" to produce the
sshfp records; switch to logging in and getting these via "ssh-keygen
-r" on the host.
Change-Id: Icb6efd7c4fd9623af24e58c69f8a188a4c1fb4c9
Add a tool to scan a host and generate the sshfp records to go into
dns. Hook this into the DNS print out from the node launcher.
Change-Id: I686287c3c081debeb6a230e2a3e7b48e5720c65a