'Change the speed (disk tier) of a disk
:param  node: The server to change the disk speed of
:type   node: :class:`Node`
:param  disk_id: The ID of the disk to change
:type   disk_id: ``str``
:param  speed: The disk speed type e.g. STANDARD
:type   speed: ``str``
:rtype: ``bool``'

def ex_change_storage_speed(self, node, disk_id, speed):

    create_node = ET.Element('ChangeDiskSpeed', {'xmlns': SERVER_NS})
    ET.SubElement(create_node, 'speed').text = speed
    result = self.connection.request_with_orgId_api_1(('server/%s/disk/%s/changeSpeed' % (node.id, disk_id)), method='POST', data=ET.tostring(create_node)).object
    response_code = findtext(result, 'result', GENERAL_NS)
    return (response_code in ['IN_PROGRESS', 'SUCCESS'])
