Session.hostkey_hash: return bytes in Python 3
Session.hostkey_hash: return bytes in Python 3

As libssh2_hostkey_hash(3) returns raw binary bytes which obviously
cannot be interpreted as UTF-8, Session.hostkey_hash shall return a
bytes object in Python 3 instead of an str object.

snoack/ssh4py,snoack/ssh4py,snoack/ssh4py