build_image: sink passed eclean flag to avoid fatal

BUG=chromium:1044411
TEST=Works Locally

Change-Id: Iaae76c2b92b2fa02f15631248790c643f59339b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/2442123
Tested-by: George Engelbrecht <engeg@google.com>
Auto-Submit: George Engelbrecht <engeg@google.com>
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Alex Klein <saklein@chromium.org>
1 file changed