Override modify to check kwargs before request sent to device.

def _modify(self, **patch):
        """Override modify to check kwargs before request sent to device."""
        if 'state' in patch:
            if patch['state'] not in ['user-up', 'user-down', 'unchecked', 'fqdn-up']:
                msg = "The node resource does not support a modify with the " \
                      "value of the 'state' attribute as %s. The accepted " \
                      "values are 'user-up', 'user-down', 'unchecked', or 'fqdn-up'" \
                      % patch['state']
                raise NodeStateModifyUnsupported(msg)
        if 'session' in patch:
            if patch['session'] not in ['user-enabled', 'user-disabled']:
                msg = "The node resource does not support a modify with the " \
                      "value of the 'session' attribute as %s. " \
                      "The accepted values are 'user-enabled' or " \
                      "'user-disabled'" % patch['session']
                raise NodeStateModifyUnsupported(msg)
        super(Node, self)._modify(**patch)