Get fido account number.

def _get_account_number(self, token, uuid):
        """Get fido account number."""
        # Data
        data = {"accessToken": token,
                "uuid": uuid}
        # Http request
        try:
            raw_res = yield from self._session.post(ACCOUNT_URL,
                                                    data=data,
                                                    headers=self._headers,
                                                    timeout=self._timeout)
        except OSError:
            raise PyFidoError("Can not get account number")
        # Load answer as json
        try:
            json_content = yield from raw_res.json()
            account_number = json_content\
                            .get('getCustomerAccounts', {})\
                            .get('accounts', [{}])[0]\
                            .get('accountNumber')
        except (OSError, ValueError):
            raise PyFidoError("Bad json getting account number")
        # Check collected data
        if account_number is None:
            raise PyFidoError("Can not get account number")

        return account_number