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>
diff --git a/build_image b/build_image
index 1c28a45..4414932 100755
--- a/build_image
+++ b/build_image
@@ -80,6 +80,8 @@
   "Toolset that this script is being used with."
 DEFINE_string version "" \
   "Overrides version number in name to this version."
+DEFINE_boolean eclean ${FLAGS_TRUE} \
+  "Noop to sink the argument instead of going FATAL: crbug.com/1044411"
 
 # Parse command line.
 FLAGS "$@" || exit 1