Be forward compatible with OpenSSH 6.8+
Be forward compatible with OpenSSH 6.8+

OpenSSH 6.8+ changes the default hash output by ssh-keygen from md5 to
sha512, and hashes are prefixed with the hash name. This updates the
testing code to force the legacy behavior if requested.

ClemsonSoCUnix/django-sshkey,ClemsonSoCUnix/django-sshkey,ClemsonSoCUnix/django-sshkey