installer: Return correct device nodes for NAND devs

On NAND device, rootfs, kernel, and other partitions have different
device names such as /dev/ubiX_0, /dev/mtdX, /dev/ubiblockX_0. This CL
changes utility functions such as GetBlockDevFromPartitionDev,
GetPartitionFromPartitionDev to return appropriate values for these
special device nodes.

BUG=brillo:39
TEST=unittest

Change-Id: I522a7c15732cfc36219c051f6c0d04e3ac558592
Reviewed-on: https://chromium-review.googlesource.com/251244
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Nam Nguyen <namnguyen@chromium.org>
Trybot-Ready: Nam Nguyen <namnguyen@chromium.org>
Tested-by: Nam Nguyen <namnguyen@chromium.org>
3 files changed