leap_cli: be able to parse both ECDSA ssh key as well as rsa key

Debian is preferring the ECDSA key over RSA now days, but the leap cli is using the RSA key. This means that if you leap ssh in to a host, it is fine because that fingerprint is managed, but if you ssh without leap ssh, you will be prompted for a different fingerprint than what is used by leap-cli because the RSA fingerprint is different than ECDSA.

I think we should switch to ECDSA now because RSA is going the way the dinosaur soon and there are rumors it is compromised :P

(from redmine: created on 2013-05-02, closed on 2014-10-29, relates #3476, relates #3740 (closed))