R1:e15fff00a640

Use "LogLevel=ERROR" to try to improve "ssh" hostkey behavior without doing anything extreme/hacky

Summary:
Ref T13121. When you connect to a host with SSH, don't already know the host key, and don't have strict host key checking, it prints "Permanently adding host X to known hosts". This is super un-useful.

In a perfect world, we'd probably always have strict host key checking, but this is a significant barrier to configuration/setup and I think not hugely important (MITM attacks against SSH hosts are…