Works only in test mode!
        Handle GET /insight-api/addr/:address/balance

def GET_confirmed_balance_insight( self, path_info, address ):
        """
        Works only in test mode!
        Handle GET /insight-api/addr/:address/balance
        """
        if not BLOCKSTACK_TEST:
            return self._send_headers(status_code=404, content_type='text/plain')

        if not check_address(address):
            return self._reply_json({'error': 'Invalid address'}, status_code=400)

        res = self._get_balance(address, 1)
        if 'error' in res:
            return self._reply_json(res, status_code=502)

        return self._reply_json(res['balance'])