Init header to values (or default values)
        :param x_auth_token: Token from Keystone for tenant_id (OpenStack)
        :param tenant_id: TenantId (OpenStack)
        :param content_type: Content-Type header value. By default application/xml
        :param transaction_id: txId header value. By default, generated value by generate_transaction_id()
        :return: None

def init_headers(self, x_auth_token, tenant_id, content_type=HEADER_REPRESENTATION_XML,
                     transaction_id=generate_transaction_id()):
        """
        Init header to values (or default values)
        :param x_auth_token: Token from Keystone for tenant_id (OpenStack)
        :param tenant_id: TenantId (OpenStack)
        :param content_type: Content-Type header value. By default application/xml
        :param transaction_id: txId header value. By default, generated value by generate_transaction_id()
        :return: None
        """

        logger.debug("Init headers")
        if content_type is None:
            if HEADER_CONTENT_TYPE in self.headers:
                del(self.headers[HEADER_CONTENT_TYPE])
        else:
            self.headers.update({HEADER_CONTENT_TYPE: content_type})

        if transaction_id is None:
            if HEADER_TRANSACTION_ID in self.headers:
                del(self.headers[HEADER_TRANSACTION_ID])
        else:
            self.headers.update({HEADER_TRANSACTION_ID: transaction_id})

        self.headers.update({X_AUTH_TOKEN: x_auth_token})

        self.headers.update({TENANT_ID: tenant_id})

        logger.debug("Headers: " + str(self.headers))