As some BIOSes try to boot only from the "first" disk, Ironic
should order potential disks not only by size, but also by name.
This patch proposes to add secondary sorting by device name when
identifying the root disk.
Change-Id: I4017c839eeb9d00d2b4ad5b90e4e9b65b74296c7
Story: #2004976
Task: #29434