Use Dracut for building ramdisks

Our current deploy ramdisks include functionality that is
duplicated from existing tools such as Dracut, and do not include
some features that those tools do.  Reimplementing our deploy
ramdisks to use Dracut would shrink our maintenance burden for
that code and allow us to take advantage of those additional
features.

Change-Id: Ibbbe1beb2d13b8ab43a9d9c32a1391a367039134
Merge "Use Dracut for building ramdisks"