cloud.rc: Warning note about changing fingerprints for SSH

[wwarriner]

A result that is surprising to first-timers and novices is what happens when using SSH to attempt connection to a reused floating IP.

The fingerprint of the key on the remote will change, and the local ssh will balk at connecting to the remote host. Ideally they'll have strict checking and the ssh won't allow the connection.

The solution is:

1. Identify the remote hostname (i.e. the floating IP or an associated domain name). The error message will explicitly state this.
2. Use the command ssh-keygen -R HOSTNAME replacing HOSTNAME with the remote hostname found in step 1.

We should add a note about this, and a DANGER admonition cautioning that the solution needs to be carefully thought through each time it is used. It should ONLY be used in cases where there is absolute trust that it is the correct solution! Otherwise we could end up connecting to a bad actor's machine.