commands: BuildRootGitCleanup ignore ref deletion error.

Newer versions of git return errors of "git update-ref -d foo" is run
and foo doesn't exist. Older versions returned without error. A git
update on some servers broke us unexpectedly.

BUG=chromium:650911
TEST=run_tests

Change-Id: Iccd6bc9bc0b52821c29928617d20dba49fd14085
Reviewed-on: https://chromium-review.googlesource.com/390432
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Ningning Xia <nxia@chromium.org>
(cherry picked from commit eb62387504ffea771d5cbef968292b458ff2cf8a)
Reviewed-on: https://chromium-review.googlesource.com/391104
Reviewed-by: Bernie Thompson <bhthompson@chromium.org>
Commit-Queue: Bernie Thompson <bhthompson@chromium.org>
Tested-by: Bernie Thompson <bhthompson@chromium.org>
1 file changed