Bug fix to authentication process on node

        logging.debug('Authenticating user %s with password <%s>' % (login,

                      password))

        try:

#TODO: authentify returns role

            role = self.server.authentify(login, password)

        except RpcError as err:

            if err.exception == 'AuthenticationError':

                logging.warning('Authentication error')

            else:

                logging.warning('Unknown error while authenticating: %s' % err)

            return False

        else:

            if role is not 'hypervisor':

                logging.warning('Bad role affected by server: %s' % role)

                return False

            else:

                return True