gs_offloader: Add Moblab support to gs_offloader.

Updates the gs_offloader to offload to a subdirectory of the
image_storage_server for Moblab devices. This subdirectory is
determined by the MAC address of the Moblab device and a UUID
stored on the stateful partition.

BUG=chromium:413383
TEST=Manually ran on Moblab, unittests. Ran locally to ensure
non-moblab usecase still works as expected.

Change-Id: Id4dc2a8b03eb6b174cb157e4d72f183dfaa39733
Reviewed-on: https://chromium-review.googlesource.com/217822
Reviewed-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Simran Basi <sbasi@chromium.org>
Tested-by: Simran Basi <sbasi@chromium.org>
3 files changed