Get a user profile.
        Reply the profile on success
        Return 404 on failure to load

def GET_user_profile( self, path_info, user_id ):
        """
        Get a user profile.
        Reply the profile on success
        Return 404 on failure to load
        """
        if not check_name(user_id) and not check_subdomain(user_id):
            return self._reply_json({'error': 'Invalid name or subdomain'}, status_code=400)

        blockstackd_url = get_blockstackd_url()
        resp = blockstackd_client.resolve_profile(user_id, hostport=blockstackd_url)
        if json_is_error(resp):
            self._reply_json({'error': resp['error']}, status_code=404)
            return

        self._reply_json(resp['profile'])
        return