Redesign make_ext4fs to incrementally generate ext4 images

Allows passing a base fs mapping file through -d which preserves the
location of those mapping in existing files

Internal Design Doc: go/incremental-ext4
BUG: 26839493
Change-Id: I05e296693429d39466d257d1d0a3daf00510dc26
Signed-off-by: Mohamad Ayyash <mkayyash@google.com>
8 files changed