Ref D10362.
We should create a TempFile that contains the appropriate known_hosts line when creating a host resource, and pass it's path into all SSH connection to that host. This ensure that we actually connect to the intended host, and we can also then remove LogLevel=quiet which means appropriate errors will display again.
Actually we might have to do this per-lease or per-connection, given that if taskmaster daemons are running across multiple machines, then the path to a known_hosts file won't be valid across all of them.
The problem with doing it per-connection at the moment is that the interface returns an ExecFuture, which doesn't provide us any way of automatically cleaning up the known_hosts file when the future resolves.
Closing this because beyond diagnosing initial configuration, there isn't much value in making things this much more complicated.