Flag to turn off host-key check

[Tobias Karlsson]

Let me start by saying that I think OpenSSH is a great tool and thanks to everyone contributing to it's existence.

However, I have a request:

I'd like to have a flag that ignores the check of the host key. I'm fully aware of that this opens up for man-in-the-middle attacks and that there is a risk of lazy users mis-using this feature, but it would be very useful for us using SSH in a lab environment where the host key of the equipment frequently changes.