chromeos-common: add partnum tool

Change-Id: Ie937d60cba4a2437da22fed4f79c48378d94d9bc
Revert "feat(chromeos_legacy): update menu.lst files"

This reverts commit a56c93c58fa4ca5bf8b7681b346d44e4811c3c6f.
fix: don't use hard coded partition layouts

instead of relying on hard coded numbers for the partition layout use
the numbers based on labels.

Change-Id: I7f9964c6028bbb0aeaec3f9f8e3b4c5b380ba76e
hack(chromeos-install): remove the kernel code

we don't have a kernel partition, just remove this code until we have a
clean way of doing it upstream.

Change-Id: I2d298ee99d72499c246dcaba1f3c47d84d1c6392