Log all available artifacts name in exception for troubleshooting

BUG=b:63058849
TEST=local run devserver

Change-Id: I77a2a0709ecf72e1dc49cc455735704e9692233a
Reviewed-on: https://chromium-review.googlesource.com/549986
Commit-Queue: Dan Shi <dshi@google.com>
Tested-by: Dan Shi <dshi@google.com>
Trybot-Ready: Dan Shi <dshi@google.com>
Reviewed-by: Kris Rambish <krisr@chromium.org>
1 file changed