xmlrpc_test: Expect bytes rather than strings for binary attributes
The attributes krbextradata, krbprincipalkey, and userpassword contain
binary data.
Part of the work for: https://fedorahosted.org/freeipa/ticket/4985
Reviewed-By: Martin Basti <mbasti@redhat.com>
Reviewed-By: Petr Spacek <pspacek@redhat.com>