[sftp] Add additional sftpProtocol::openConnection() for libssh 0.8.3+
Summary:
This uses the new known_hosts API and creates SHA256 fingerprints for
public key verifcation.
Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Differential Revision: https://phabricator.kde.org/D16538