Extend device hints with disk name

Having disk name (like sda) as a part of VALID_ROOT_DEVICE_HINTS simplify deployment of BM with not trivial HDDs configuration. As an example we have servers with 14 x 400 GB SSDs or 12 x 4TB + 2 x 600GB. And it is nearly impossible to specify correctly which disk to write the image to (especially if HW raid is built) with any device hint option provided by the Ironic at the moment. Also having such an option helps disk replacement use case.