cgpt.py: Add fs_options flag to the disk_layout.json file.

The fs_options flag allows to pass command line options to the
program that format the filesystem. These options are specific to
the fs_format, so a dictionary can be speficied allowing different
default options for different filesystems.

BUG=chromium:282703,chromium:382951
TEST=./build_image --board=link still works.
    `cgpt.py readfsoptions base disk_layout.json 3` also works.

Change-Id: Id0b1abb1637a08621a8f216619868be0e49d4e6b
Reviewed-on: https://chromium-review.googlesource.com/236997
Trybot-Ready: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
3 files changed