Get number of clients.  Uses HEAD to /clients interface.

        :Returns: (int) Number of clients

def client_count(self):
        """
        Get number of clients.  Uses HEAD to /clients interface.

        :Returns: (int) Number of clients
        """
        response = self._head(url.clients)
        self._check_response(response, 200)
        return int(response.headers.get("x-client-count", -1))