autoupdate: Set the hash_sha256 in devserver (omaha) response

The new changes in update_engine requires the new hex based sha256 hash sent by
omaha to be checked. But, currently in devserver we only sent base64 ecndoed
sha256. This CL adds hash_sha256 in the package tag of the response by
calculating the hex based sha256 hash of the payload.

BUG=chromium:821599
TEST=cros flash

Change-Id: I4449d90513db2dcd1424a6693ec7ce172135d689
Reviewed-on: https://chromium-review.googlesource.com/961586
Commit-Ready: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Xixuan Wu <xixuan@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
1 file changed