As part of the blueprint root-device-hints Ironic will pass some to the
deploy ramdisk some hints about which disk device it should pick to be
root device (the one where the image will be deployed on).
Before the deploy ramdisk would pick the first device it finds, but as the
machine could have more than one SATA, SCSI or IDE disk controllers the
order in which their corresponding device nodes are added is arbitrary
causing devices like /dev/sda and /dev/sdb switching around on each
boot time.
Plus, as people are adding support to build RAID arrays in Ironic we need
a way to tell it to use the just created device to be the root device.
The list of hints that could be passed to the deploy ramdisk so it finds
the right disk is:
* wwn (STRING): unique storage identifier
* serial (STRING): disk serial number
* model (STRING): device identifier
* vendor (STRING): device vendor
* size (INT): The size of the disk in GB
If not hints are passed, the deploy ramdisk will continue to do what it
did before to find the disk.
Change-Id: I8425f593e1a610af5a3697988702603ff218f2de
