When no root_device hint is set, an MDRAID partition can be incorrectly
selected as the root device which causes installation of the bootloader
to the physical disks behind the MDRAID volume to fail. See the notes
in the referenced Story for more detail.
This change adds a little more specificity to the listing of block
devices.
Change-Id: I66db457e71a0586723ee753bef961aec5bf58827
Story: 2007905
Task: 40303