Add utility function to general_installer

Add functions for resetting partition table and resetting stateful
partition to general_installer.

Since these functions are used to reset system devices, an unittest is
not available.

BUG=chrome-os-partner:21938
TEST=Compile succeed

Change-Id: I5fb00ac8721597703ca6d325ced136f508e39f1a
Reviewed-on: https://chromium-review.googlesource.com/67045
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Chun-Yen Ho <chho@chromium.org>
Tested-by: Chun-Yen Ho <chho@chromium.org>
2 files changed