Allow server creation with no SSH key pair

[j-rewerts]

I may be out to lunch on this, but it looks like we currently require an SSH keypair to start our ssh-server. Guessing we mount the key into our container on startup? In Browsh's issue #188, it could help this user to simply be able to run the image with no keypair setup. Is this possible? It looks like gliderlabs SSH library supports it.

[tombh]

Yes, this is exactly right. The only reason that I mount keys is so that users don't get that "unkown host" warning every time Kubernetes changes the SSH server's Docker container. So it should be easy to add a flag to simply not use the hostKeyFilePath arg.

(BTW, I've actually got my original Browsh dev system back up and running), so if I get some time I can actually make pull requests again :)