autoupdate_EndToEnd: Enable imaging with source payload in Brillo.

BUG=b:24158510
TEST=Source image installed in moblab run.

Change-Id: I39dea1af1223c6bd80e186482c982c96b958fe0c
Reviewed-on: https://chromium-review.googlesource.com/304935
Commit-Ready: Gilad Arnold <garnold@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
1 file changed