This matches the ssh-add command for identity keys,
it will add the host key to the ssh known_hosts file.
If a ssh key for the host already exists in the file,
it will not be added again so can be run multiple times.
This is similar to the existing minikube "ssh-key" command, but gets
the content of the host key instead of the path to the identity key.
The output of this command can be added to the ~/.ssh/known_hosts,
for strict host key authentication. For instance when using Docker.
minikube-bot
Anders F Björklund
Steven Powell