Add `#signature_algorithm` and update `#ssh_do_sign` and `#to_blob`
Add `#signature_algorithm` and update `#ssh_do_sign` and `#to_blob`

    Modifies `OpenSSL::PKey::RSA` to provide a `#signature_algorithm`
    method which provides the signature algorithm value expected by
    OpenSSH. The `#ssh_do_sign` method is updated to use the set
    algorithm (SHA256) and `#to_blob` is updated to include the
    signature algorithm instead of the key type.

sni/vagrant,sni/vagrant,sni/vagrant,sni/vagrant